Expanding my mineral collection I: Gold, rose quartz, Tiger's Eye, amethyst, blue agate, fluorite and celestine

Fig.1.1 - My mineral collection, as of 2022 ✨💎

Fig. 1.2 - The mineral specimens inside the wooden box on the left, in Fig. 1 above

In my last post I wrote about wanting to blog about science more, so here's the start of a new series about another science topic I like - Mineralogy, the subject of geology specializing in the study of the chemistry, crystal structure and physical properties of minerals ✨💎. I have been a great fan of collecting minerals and gemstones since I was little, and through the years I've collected quite a few, both from various shops and from field trips, as you can see in the pictures above (Figs. 1.1-2) 😃 

Back in Primary School, I was so into mineralogy that at one time I was seriously considering it as a career, alongside Astronomy and painting - Yep, all three at the same time, I even wrote a schedule about it 😅 😂, and the fact I've always been interested in so many things (often with multitasking as a result 😬) has been both great (boredom? What is that?) and a bit of the bane of my life (never enough time xD). But I ended up choosing Astrophysics as the career, so for now mineralogy is just a hobby.

Fig. 2.1 My mineral collection area, as of March 2024.

 A hobby that stayed a bit more on hiatus throughout the 2010s, until I wanted to get back into it more actively since 2021. But what really gave me the final nudge was finding out that the local kiosk was selling a mineral collection, the National Geographic RBA minerals collection (in Spanish), and it included a lot of minerals and gems I didn't have. So in April 2022 I started collecting most of the weekly numbers, and here I am, full on back to mineralogy as a hobby and expanding my existing collection 😃:

Fig. 3.1 - New specimens from the National Geographic/RBA mineral collection (as of mid-August 2022). Except for the amethyst, which I already had, and the sodalite, which is an specimen that I also already had, replacing the subpar one from the collection xD.

Fig. 3.2 - New specimens from the National Geographic/RBA mineral collection (as of January 2023).

Fig. 3.3 - Most of the boxes from the National Geographic/RBA mineral collection (as of March 2024).

So I thought it would be interesting to blog about each of the minerals in this collection in a new series where I talk about a handful each at a time, following the order of the National Geographic/RBA collection. And as well as including the pieces from this collection and expanding a bit about what mineralogy has to say about them, and some tidbits on the history and STEM applications of each one, in these posts I will also be including the specimens from my existing collection before I started with this one, and will also be editing the posts in this series routinely to add new acquired pieces from separate hauls. So this series can be seen as a 'mineral collection compendium' of sorts, and some will consequently become quite long 😅. But if minerals are your thing, read and look on!

Also, because I started the collection when it had already been selling in kiosks for a while (Number 8, fuchsite, was the first one I got back in April), when I initially published this first post I didn't have all of the collection specimens for numbers 1-7 of the collection. In this first version, I followed the order anyway, omitting the ones that I didn't have as yet from the RBA collection, and showing the existing specimens from my collection for the ones that I already had ✨💎. But I ended up getting all these first numbers that I didn't have yet because perfectionism who xD, so this post has been updated to reflect that. As a result of adding new pictures afterwards, the figure numbering in this first post is not as coherent as I'd like as a result, though, but ah well, bear with me. Also, this one turned into a veritable masterpost in its length because I now talk about 7 minerals instead of the 4-5 of subsequent posts in this series, and this post also includes some of the most ubiquitous minerals in my collection, such as amethyst and fluorite, of which I keep adding new pieces xD.

-Brief (related) intermission: The bane of 'Crystal healing' and pseudoscience

And before we delve into it, let me write a quick rant about how difficult it is to search for infographics and charts of minerals that have to do solely about mineralogy, gemology and science - When you ask a search engine to give you info about a mineral or a gemstone, most of the time the first results of the search include info about the 'healing power of crystals', 'crystals and the horoscope', 'the best crystal for your mood', 'the benefits of crystals for your health', and so on and forth, and yeah, I have so little patience for pseudoscience as a rule, I just want a scientific infographic about the mineral or gemstone, not a list of how supposedly this 'crystal' is going to help me with my current mood or my health problems 🙄 (I mean, I wish that my collection would help alleviate my chronic gastritis, but unfortunately they don't work that way 😅 xD). 

I guess I would also have way more tolerance for all this 'metaphysical', 'mystical', 'esoteric' and 'spiritual' content if it really didn't do any harm, if it were just a pastime that wouldn't affect anyone negatively and didn't promote anything dangerous, same as I like to collect minerals and gems because I like mineralogy and that's perfectly harmless both to me and everyone else - unless I threw the largest specimens at someone, which a collector wouldn't do anyway 😅🤣 (and well, there's also the issue of the environmental damage and labour exploitation which often occurs when mining for certain minerals and gems is in high demand, but that is another whole can of worms, and I highly suspect that the jewellery, construction, and yes, the increasingly 'trendy' 'spiritual-esoteric-New Age' industries are much more relevant to this matter than the pieces aimed for mineralogy researchers and collectors. Although every bit does count, as the mining conditions are often basically the same disregardless of the use the minerals will be given, we mineral collectors probably end up buying many specimens from the 'New Age' industry anyway, and humans are regrettably very adept at destroying the planet in every way and exploiting other humans :S). 

The thing is, this trend of 'healing crystals' is hardly harmless. It's just inherently dangerous to promote the idea that rocks and crystals can actually affect a person's health concerns or their mood just by them touching their skin, wearing them, having them close in their home, or meditating on them :S. 'Crystal healing', same as any other pseudoscience, can actually convince many people not to seek actual medical treatments for their particular ailments 😤, and that is something that everyone should not take lightly. That is why I am so against people promoting pseudoscientific spirituality or alternative medicine as if it was actually both effective and harmless, when it's really neither, and there's no scientific basis that minerals and gems can affect a person's mood or health. 

Sure, some 'therapeutical' practices rooted in the spirituality world can actually help to alleviate stress and anxiety, but more because of the often relaxing ASMR quality of them, if you will, rather than because the supposed 'energy transfer' of these 'crystals' directly affects someone's mood and health (spoiler alert, it doesn't). Even though I don't view it as spiritual in any way, collecting minerals and feeling their weight and textures actually does help with my anxiety as well, but that's what it is, it's relaxing and grounding, same as drawing or playing music could be, and I find minerals and gems to be beautiful and visually pleasing, with their colours and shapes. And I'm interested in knowing how they were formed and what their properties are, and about the scientific explanation for these colours and shapes. Which is more than enough to help. 

But to go from there to saying that 'crystals' can cure actual illnesses and affect your moods and that their 'energy' helps your anxiety is pure placebo at best and deadly at worst 😬. Like, some people in 2020 when the current pandemic started actually believed that carrying crystals in their pockets would protect them better than wearing a mask 🤔🤪, as if they were regressing to the point during the 14th Century's Black Death pandemic where people also believed that walking the streets smelling flowers in bouquets (posies) and pomanders would actually protect them from catching the 'miasmas of the plague' ('Miasma theory' had literal aromatherapy as both the prevention and cure for the bubonic plague xD). Once again, a mask would've worked much better 😅 (although at least they were trying to block their noses with something, it's maybe marginally better than carrying a stone in your pocket as an amulet xDD)

 

But more about my pet peeves with pseudoscience in probably another post xD, as today we've got minerals and gems to talk about xD 💎: 

Also note, as explained above, that the posts in this mineralogy series will be updated with pictures of the new specimens that I get in separate hauls (which will also have their own post).

Fig. 4 - Numbers 1-3 in the National Geographic mineral collection

Fig. 5 - Numbers 4-5 in the National Geographic mineral collection

1) Gold: Apart from a couple of jewellery pieces (rings, basically, but not that One gold Ring xD), the RBA specimen of a small bottle with gold flakes in an alcohol solution (originating in Spain, one of the main gold mining places since Ancient Times), in Figs. 5.51-2, is the first addition of gold to my mineral collection:

Fig. 5.5.1 - Bottle of gold flakes from the RBA mineral collection

Fig. 5.5.2 - Bottle of gold flakes from the RBA mineral collection

💎A bit about gold: Source 1, Source 2, Source 3, Source 4, Source 5

Fig. 5.5.3 - Source

Gold is a chemical element, a mineral and a precious metal (symbol Au, from Latin aurum). A transition metal in the group 11 of the Periodic Table, it is one of the higher atomic elements (79) to occur naturally.  Native gold typically occurs as denditric growths, as small to microscopic grains embedded in rocks and hydrothermal veins (often alongside quartz and sulfide minerals such as pyrite, used as an ore of gold), as well as in the form of grains, flakes and larger nuggets in alluvial deposits (having been eroded from rocks, collected in rivers and often welded into nuggets by the water). Well-formed gold crystals, in either octahedral or dodecahedral form, are very rare. While small amounts of gold can be found almost everywhere worldwide, large deposits are only to be found in limited locations. 

Gold is one the most highly prized metals in most societies (and thus one of the most expensive), because of its bright and attractive orange-yellow colour, its rarity, and its many properties and uses (as we will see below in the trivia section). Gold in its pure form is dense, soft and ductile, the most malleable of all metals. It can be hammered into sheets so thin gold becomes semi-transparent, and drawn and stretched into incredibly thin wires. It is also one of the least reactive chemical elements, as it is very resistant to tarnishing, corrosion, surface oxidation and most chemical reactions, and easily alloys with many metals. It also proves to be a good conductor of both heat and electricity.  

✨Interesting historical and STEM trivia of gold:  

• Etymology: The work "gold" is cognate with similar words in several Germanic languages, originating in the Proto-Germanic *gulþą, from Proto-Indo-European *ǵʰelh₃- ("to shine, to gleam; yellow").  The symbol Au representing gold in the Periodic Table comes from the Latin word for gold, aurum (Proto-Indo-European *h₂é-h₂us-o-, "glow").
  

• Gold has been used by humanity for coinage and jewellery and decorative purposes throughout recorded history, and it appears to have been the earliest metal used in crafting (for example, small amounts of natural gold have been found in Spanish caves used during the Paleolithic, c. 40,000 BC, and the earliest gold artifacts known date from 4600 BC to 4200 BC). Almost every culture has considered gold to be a prominent symbol of power, status, beauty and 'perfection'.

• 🌟🪐Astrophysics fact! Gold is thought to have been originally produced in supernova nucleosynthesis, and, more recently, it has also been suggested that gold and other elements heavier than iron may also be produced as a result of the collision of neutron stars.
  

• Ancient and Medieval alchemy has long sought to investigate the possibility of producing gold from a common element such as lead (transmutation of the elements), via the interaction of the mythical 'Philosopher's Stone'. Thanks to the study of nuclear physics in the 20th century, gold can be now synthesized - This was achieved in 1924 by Japanese physicist Hantaro Nagaoka, and afterwards in 1941 by a USA team, obtaining radioactive gold isotopes from mercury by neutron bombardment. In 1980, Glenn Seaborg also succeeded in transmuting bismuth into gold. However, the manufacture of gold via nuclear transmutation proves to be uneconomical, far exceeding the value of the gold created.

•  Pure gold can be ingested due to it being non-toxic and non-irritating, and it is sometimes used as food decoration in the form of gold leaf, flakes or dust, especially for desserts and drinks. Gold flakes in food were used by Medieval nobility to showcase their power and status, and nowadays it is similarly sometimes used to decorate expensive gourmet dishes. Gold has no taste and provides no nutrition, and so, barring curiosity to try such a dish, the  exorbitant prices of dishes and drinks that include decorative gold (even though gold flakes and gold leaf are not *that* expensive in the small quantities typically used, actually!) are aimed at the exact same demographic: Rich, privileged people reinforcing their status and ego by eating an incredibly expensive dish unnecessarily decorated with a rare precious metal that tastes of nothing...simply because they can 🙃
  

The current uses of gold are many and varied: From jewellery and decoration, to coinage, and various industrial and medical uses:

• Jewellery and decoration: The manufacture of jewellery and ornamental objects has been the main use of gold throughout thousands of years. Its yellow colour and high luster, as well as its resistance to tarnishing and great malleability and ductility makes it an ideal candidate for jewellery making. However, the softness of pure gold also poses challenges, which can be solved by alloying gold with silver, copper or platinum to increase its hardness and durability. The gold proportion of these alloys is measured in karats (k). Thus, pure gold corresponds to 24k, and an alloy of 75% gold by weight is labelled as 18k, for example (as 18/24=75%). As well as jewellery, gold is also made into thread to be used in decorative embroidery, and gold hammered into thin sheets (known as gold leaf) can be used to gild furniture, statues and buildings.
  

• Coinage: Due to its high value and rarity, gold has been used for a long time to exchange money in the form of coins, with the first known use of gold pieces as monetary transactions dating back to 600 BC in Asia Minor. Gold coins are no longer in use today as an official currency, being created just as commemorative or collectible items.

• Industry: Approximately 10% of the yearly produced gold goes to industry, and the main industrial use of gold is in the manufacture of electronics, and most especially its ample use as electrical connectors, due to gold's conductivity and resistance to chemical reactions such as corrosion. Thus, many electronic devices include a small amount of gold, from cell phones to computers, GPS units, television sets and calculators. Gold is also vastly utilized in the aerospace industry: It plays an important part in spacecraft circuitry as connectors, and thin films of gold are also used as a lubricant between mechanical parts. In addition, gold-coated polyester films are used to reflect infrared radiation and stabilize the spacecraft temperature, and the visors of astronaut helmets are often coated with a thin film of gold to help reflect solar radiation, protecting the astronaut's eyes and skin.
  

• Medical: Historically, gold has been used for a long time for medicinal and dentistry purposes, since ancient and Medieval times - and not always in the most scientific way, as gold has been always associated with 'beauty', purity and perfection', and thus, it was concluded that consuming it had to be beneficial and healthy 😅. In the 19th Century, gold was used as therapy for various nervous disorders, as it was considered to be an anxiolytic. Even though historical medical knowledge was not always on point, gold has various legitimate medical uses nowadays: As well as playing a part in the manufacture of medical instruments and electronic equipment, gold is still used in dentistry for fillings, crowns and other orthodontic procedures; weak solutions of gold salts have proven to have anti-inflammatory properties, and are used to treat several medical conditions such as rheumatoid arthritis; and radioisotopes of gold are also being used for oncological diagnosis and treatment.
  

• Hazards:  Gold mining and production contributes to environmental pollution, featuring cyanide spills from gold mines, and large amounts of ore waste dumps including several hazardous elements (lead, arsenic and mercury, for example). Gold extraction also requires nearly 25 kWh of electricity per gram of gold produced.

Fig. 5.5.4 - Gold infographic from the RBA collection (in Spanish)

2) Rose Quartz:

Fig. 6.1 - 3 small specimens of rose quartz from my existing collection

Fig. 6.2 - A larger rose quartz in my collection

Fig. 6.3 - A larger rose quartz in my collection

Fig. 6.4 - The rose quartz specimen from the RBA collection

Fig. 6.5 - The rose quartz specimen from the RBA collection

Fig. 6.6 - Three specimens of rose quartz, minus the RBA one, alongside a Tiger's Eye and a dyed blue agate

In my existing collection, I had four specimens of rose quartz (Figs. 6.1, 6.2-6.3, and 6.6): The one in the box in Fig. 6.1, from Brazil, is part of an assorted gemology collection (which you can see in the left in Fig. 1 above) that I got in the science shop of the former CosmoCaixa museum. The other tumbled stone in the left I got from your typical 'New Age shop' (although I've been to some actual mineral shops advertised as such, mineral specimens, tumbled stones, crystals and gems are usually found in 'New Age' shops, and in stalls that highlight the 'spiritual' nature of the stones 😅), and the one in the right, the only unpolished sample I have, was part of my very first mineral collection I had when I was little. This one and the larger rose quartz in Figs. 6.2-6.3 are quite similar to the advertised rose quartz in the National Geographic collection (a specimen from Brazil which I recently got now the collection's getting started again at kiosks, see Figs. 4 and 6.4-6.5), only larger. 

A video with some of these rose quartz in the Sun:

💎A bit about rose quartz: Source 1, Source 2, Source 3, Source 4, Source 5, Source 6, Source 7, Source 8, Source 9

 Firstly, seeing as all the minerals that I'll be talking about on this post (rose quartz, Tiger's Eye, amethyst and blue agate) are different varieties of quartz, let's introduce quartz as a mineral first:

 Quartz is a hard, crystalline mineral composed of silica (also known as silicon dioxide, with a chemical formula of SiO₂). The second most abundant mineral on Earth's crust (behind feldspar), it can be found ubiquitously in all parts of the world, is abundant in igneous, metamorphic and sedimentary rocks, and it's the primary constituent of sand in beaches, deserts and riversides. Quartz has two forms, macrocrystalline quartz (visible crystals, in the trigonal or hexagonal system) and cripto/microcrystalline quartz (microscopic crystals).  The ideal quartz crystal shape is dipyramidal prismatic (a six-sided prism terminated with six-sided pyramids at each end), but many quartz crystals are twinned (sharing some of the crystal lattice points symmetrically), in druzy aggregates (short-prismatic crystals often lacking prism faces), intergrown to a degree that they only show part of their crystal structure, or lacking apparent crystal faces altogether (massive habit).

    Many different varieties of quartz exist, several considered as gemstones and semiprecious stones, and they are classified both according to colour and microstructure. Macrocrystalline quartz varieties include rock crystal, milky quartz, rose quartz, amethyst, citrine, smoky quartz, prasiolite, blue/dumortierite quartz, aventurine, and rutilated quartz; while microcrystalline quartz, or chalcedony,  include varieties such as agate and jasper, carnelian, Tiger's Eye, chrysoprase, and heliotrope.

See this page for more info on the different uses of quartz, including their widespread use in different industries, and particularly their marked utility in making time-keeping instruments, electronic products and devices, and optical instrumentation.

✨Some interesting trivia about quartz:  

•  The word "quartz" comes from the German Quarz, of Slavic origin, and corresponds to the Czech term tvrdý ("hard").
  

•  In Ancient Greece, quartz was referred to as κρύσταλλος (krustallos), derived from κρύος (kruos), which means "ice, icy cold". This is because several philosophers and naturalists (including Theophrastus, and later also Roman naturalist Pliny the Elder) believed that quartz was a form of supercooled ice, ice that had been permanently frozen after a great period of time 😱. The word "crystal" also comes from the Greek κρύσταλλος. This idea actually persisted for a long time, until at least the 17th Century!
  

•  In the Irish language, the name for quartz is grianchloch, "sun-stone". This mineral was used notably used in Prehistoric Ireland (as well as other countries) to create stone tools, and it is also regularly found in European burial sites such as Newgrange in Ireland.

• In Europe and the Middle East, the different varities of quartz have been the semiprecious stones most commonly used for jewellery and carvings, while jade holds this title in East Asia and the Pre-Columbian-colonization American civilizations.
  

• In the 17th century, Nicolas Steno's study of quartz paved the way for modern crystallography. The piezoelectric properties of quartz were discovered by Jacques and Pierre Curie in 1880, and the quartz oscillator or resonator was first developed by Walter Guyton Cady in 1921. By the 1930s, the electronics industry had become dependent on quartz crystals.

Fig.7 - Source

 Rose quartz and pink quartz (sometimes used to refer solely to the transparent types, also see below), is the first quartz variety which will appear in this post, referring to pink-coloured quartz specimens with hues ranging from pale pink to a vivid medium-dark rose red (especially in some larger specimens). Being hard and abundant, rose quartz has been commonly used in jewellery.

 Rose quartz is most commonly found as massive aggregates, with prismatic crystals being considerably rarer. In fact, some recent classifications differentiate between 'rose quartz' and 'pink quartz', with crystals having never been found for the former variety, and the latter occurring in well-formed and transparent prismatic crystals in similar pink hues.

Formerly, the pink colour of rose quartz  was continuously attributed to trace amounts of titanium (Ti), iron (Fe) or manganese (Mn). However, recent X-ray diffraction studies instead suggest that the hues of rose quartz are rather attributed to microscopic fibrous inclusions of a pink variety of the mineral dumortierite, and these inclusions are often abundant enough so as to make rose quartz appear translucent more often than transparent. On the other hand, the transparent pink quartz variety instead gets its pink hues as a result of traces of aluminum (Al) and phosphorus (P) replacing silica (Si) in the atom lattice.

Sometimes, rose quartz presents asterism (star rose quartz), caused by microscopic rutile fibrous inclusions which produce a six-rayed star in transmitted light if the gem is cut in cabochons or spheres. Rose quartz is also dichroic, changing its colour from paler to more intense pink depending on the direction of the transmitted light.

causes visible light to be split up into distinct beams of different wavelengths (colours) (not to be confused with dispersion), or one in which light rays having different polarizations are absorbed by different amounts.^[1]

✨Some interesting history and mythology trivia about rose quartz:  

•  Rose quartz beads have been found in modern Iraq (ancient Mesopotamia) dating back to 7000 BC, and jewellery with rose quartz was also crafted by the Assyrians in 800-600 BC. 
  

• Several ancient civilizations such as the Ancient Egyptians, Greeks and Romans believed that rose quartz had magical powers and used this stone as talismans (religious superstitions and mythological associations which should not be taken at face value today, *cough* 'healing crystals' current *cough* 🙃). Ancient Egyptians believed that the stone had restorative qualities and could prevent aging, and associated it with the goddess Isis, deity of life, fertility and motherhood. Ancient Greeks, for their part, associated rose quartz with Aphrodite and his son Eros, deities of sexuality, desire and fertility, while Romans used this gem to signify ownership.
  

Rose quartz infographic from the RBA collection (in Spanish)

Real or dyed rose quartz?

Fig. 8.1 - A "rose quartz" pendant cut in a faceted ball shape, which is actually an agate and quartz geode that's been dyed pink, not a true rose quartz specimen.

 Regarding pendants, I recently got two, firstly a polished rose quartz pendant (Fig. 8.3), featuring the characteristic uniform pale pink tone of many rose quartz specimens, as well as another 'rose quartz' pendant (Figs. 8.1-3), which is actually a dyed agate featuring a visually interesting small geode with some small rough quartz crystals inside, in contrast to the polished exterior, cut into a faceted ball shape. The pink hue of this pendant looks very vibrant and artificial in some places, and the piece shows the characteristic banded pattern of agate, so this one is definitely a banded agate that has been dyed pink to (poorly) imitate rose quartz. Agates are also routinely dyed in various vibrant fantasy colours to make them 'more attractive' to the regular buyer. Rose quartz is quite abundant in its natural form, with hardly any need to fake it with dyes, but, like we have seen in Figs. 6.1-6.6 and in Figs. 8.2-3, it usually showcases light pink hues, sometimes almost white, rather than vibrant pinks (darker and more intense rose hues - albeit not neon-level vibrant - can be found naturally, but are much rarer, and way more expensive). So some people might think that a more vivid colour, obtained affordably, would make for a more attractive and marketable gem, same as what does happen in other cases, especially when it comes to agates (as we will further see below in this post).

Fig. 8.2 - Real rose quartz, left (featuring a rough specimen and a tumbled stone), featuring uniform light pink hues in massive habit, vs the dyed agate  pendant, right, showcasing a brighter pink hue that is uneven, with blatant zones of nearly neon vibrant pink.

Fig. 8.3 - Real rose quartz polished pendant (above, and right), once again featuring uniform light pink hues in  a massive habit, vs the dyed agate pendant, (below, left).

Another thing that I believe factored in the decision to dye this specimen pink, maybe to imitate rose quartz (or maybe just to dye one more white/grey agate a more vibrant colour xD) is the fact that the crystal habit of rose quartz is primarily massive (crystal aggregrates with no characteristic external shape), as we've also seen above, and individual crystals (including geode specimens) are thus much rarer (and, if we assume the rose vs pink quartz classification explained above, then crystals have never been found for the rose quartz variety in the first place). I assume that someone must have thought that a faceted 'rose quartz geode' like this could look very marketable, more so than a standard agate+quartz geodine, so I guess that's why this piece was dyed (although not very expertly, unless having some neon pink zones in some of the facets was what they were intentionally going for 😅), using a much more affordable and easily found agate.

And I'm typically fine with dyed specimens, it's all about personal taste (I personal don't prefer them - this one is pretty, but I would have preferred the natural-coloured geodine, to be honest xD). My only qualm is that the manufacturers and vendors are often hardly transparent about which specimens are natural, which are dyed and which are colour-treated in other artificial ways 😕 (as we'll see below in this very collection, with the allegedly 'natural' (it's not) bright blue agate 😅).

3) Tiger's Eye:

Fig. 9.1 -  My specimen of Tiger's Eye

Fig. 9.2 -  My specimen of Tiger's Eye from the RBA collection

Fig. 9.3 -  My specimen of Tiger's Eye from the RBA collection

 

Fig. 9.4 - Although quite small, I think this Tiger's Eye is one of the most beautiful specimens in my collection

Fig. 9.5 - Tiger's Eye (including the RBA specimen) and Ox's Eye in my collection

Fig. 9.6 - Tiger's Eye (including the RBA specimen) and Ox's Eye in my collection

  I really love Tiger's Eye (chatoyancy, see below, looks so pretty), and before I could get the corresponding number from the RBA collection (featuring a specimen from Spain, in Figs. 9.2-3 and Figs. 9.5-6), I already had another Tiger's Eye in my existing collection (Figs. 9.1, 9.4 and Figs. 9.5-6), and it was also part of my very first mineral collection I had when I was little. I just love the silky look and the amber colours of this quartz variation! I also have an Ox's Eye, the variant of Tiger's Eye with red and reddish brown tones (see Figs. 9.5-6 above, as well as below, Figs. 11.1-3).

💎A bit about Tiger's Eye: Source 1,  Source 2, Source 3, Source 4, Source 5, Source 6

Fig. 10 - Source

Tiger's Eye, also known as "Tiger Eye", is a semiprecious gemstone in the quartz group, with a silky lustre and a range of hues going from golden, amber and honey to red-brown. When polished as a cabochon (rounded with a flat base), Tiger's Eye displays chatoyancy ('cat's eye effect'), an optical reflectance effect which shows a single and sharply defined band of light moving across the stone when it is rotated and moved back and forth in incident light (see the videos below for a demonstration of the chatoyancy effects of my specimen). Chatoyancy arises in this case from the structure of this gemstone's material, an intergrowth of microcrystalline quartz crystals (chalcedony) and altered amphibole fibres, such as riebeckite. Tiger's Eye forms when a variant of riebeckite, crocidolite (also known as blue asbestos), is replaced in a rock with the fibrous crystals of chalcedony. 

A 'Hawk's Eye' tumbled stone, with a mix of dark-blue and golden-coloured fibrous crystals

 

Tiger's Eye (below), Ox's Eye (red, left) and Hawk's Eye (dark blue, above) tumbled stones. Source.

 

The golden hue of Tiger's Eye is caused by the iron oxide content present in crocidolite. This mineral actually forms dark-blue fibrous crystals in its natural form, present in a variant of Tiger's Eye named 'Falcon's Eye' or 'Hawk's Eye'.  Another variation of Tiger's Eye is red in colour, called 'Ox's Eye'. This gem can occur naturally, but it is typically created artificially by heating Tiger's Eye specimens, as a result of which part of its iron content is transfomed into hematite, which has a naturally red streak (see my specimen in Figs. 9.5-6 and Figs. 11.1-3, and also see the videos below, to see its chatoyancy). Due to its lustre and its undulating bands of colour, Tiger's Eye and its variants are mainly used for jewellery and ornamentation. 

 

Fig. 11.1 - A tumbled Ox's Eye specimen, showing a lovely chatoyancy band pattern and rich reddish and bronze hues, from a September 2023 local fair. In the background we also have a vanadinite, labradorite, malachite and smoky quartz.

 

Fig. 11.2 - A tumbled Ox's Eye specimen from a mineral stall at a September 2023 local fair.

Fig. 11.3 - A tumbled Ox's Eye specimen from a mineral stall at a September 2023 local fair.

 Red Tiger's Eye (Ox's Eye) bead necklace (below, in Figs. 11.4-5), alongside my amethyst necklace in the same collection. Not all of the beads show chatoyancy and some look a bit matte and strange-patterned, not sure if it is because this Tiger's Eye is lower-grade, or because not all of the beads might be legit :S Still, it's very pretty!

Fig. 11.4 - Red Tiger's Eye (Ox' Eye) and amethyst bead necklace.

Fig. 11.5 - Red Tiger's Eye (Ox' Eye) bead necklace.

 

  Finally, here are a couple of videos showcasing the silky lustre and chatoyancy of these specimens:

 

 

 

 

✨Some interesting history and mythology trivia about Tiger's Eye:  

•  Due to its colours and its chatoyance effect, this gem ressembling a feline's eye has historically been associated with tigers, lions and cats in several cultures, from Ancient Egypt to China. In the mythologies and religions of these cultures, felines are often associated with strength and protection, and so they believed that this gem would channel strength, ward off 'evil eye' and curses, and grant protection, abundance and good luck  

(once again, modern 'crystal healers', a word, if I may - this is not actually what gems do scientifically 🙃. Being spiritual and wanting to express that through mythological and religious connections to gems is obviously fine, to each their own, *but* stating that gems can actually affect someone's health, luck and so on is, I repeat, factually wrong, it's pseudoscience and it's mumbo-jumbo. It was factually wrong when the Ancient Egyptians believed it and it is factually wrong now, and conflating spirituality, superstition, religion and myth with medicine or science is where a very dangerous problem has always lied). 

• Due to its golden hues, Ancient Egyptians also associated this stone with Sun God Ra, a deity of fertility, life-force, foresight and power. Pharaohs and aristocrats would wear Tiger's Eye jewellery believing, once again, that the gem would grant them vitality and strength. Other solar feline goddesses associated with Tiger's Eye were, of course, Sekhmet and Bastet.
  

• This belief can also be found in Ancient Rome, where Roman soldiers would carry an engraved object made with Tiger's Eye with the belief that it would protect them in battle and grant them strength. 

Tiger's Eye infographic from the RBA collection (in Spanish)

4) Amethyst

Fig. 12.1 - Nearly all the amethyst in my possession, prior to the RBA collection 😅🤣💜 4 amethyst druses of different sizes, a tumbled stone specimen, and a bead necklace I use for my late 14th Century reenactment.

Fig. 12.2 - My specimen of amethyst from the RBA collection.

Fig. 12.3 - My specimen of amethyst from the RBA collection. This piece features small black goethite inclusions.

Fig. 12.4 - My specimen of amethyst from the RBA collection, with small black goethite inclusions.

Amethyst is in one of my favourite minerals and gemstones 💜, both because purple is among my favourite colours and also because I really, really like the sparkly crystals in quartz clusters (a dense agglomeration of crystals) and druses (a rock cavity lined with a crust of projecting crystals). So yeah, I already had a lot of amethyst in my collection (Fig. 12.1, and Figs. 13-16 below), including two large amethyst druses and two smaller clusters (one of them a boxed specimen from Uruguay), as well as a tumbled stone specimen (from Brazil) that was part of my assorted gemology collection from the former CosmoCaixa museum; a hairpin; two pendants (one polished, one rough), in Figs. 16.1-2 below;  and a bead necklace (see Fig. 12.1) that I use for my late 14th Century reenactment (bead necklaces made out of semiprecious gems such as carnelian and amethyst, as well as other materials like coral, pearls and amber, were in fashion). Then there's the specimen from the RBA collection (Figs. 12.2-12.4 above), also from Brazil.

Among these amethyst druses, my favourite is the larger one on the left in Fig. 12 (and Figs. 13-15), with a more intense violet colour. This darker violet is also present in the small specimen in the bottom right in Fig. 12, part of the small boxed specimens which I keep in the wooden box on the left in Fig. 2.  The largest druse on the right is a lighter violet in colour (also in Fig. 16), similarly to the smaller druse on the bottom left. This smaller druse is actually quite similar in both colour and size to the specimen from the RBA collection (Figs. 5, 12.2-12.4), and, prior to getting the amethyst from the new collection, I actually added this one to the first box of the expanded collection, as seen in Fig. 3 (even though I already had it from before, but it looks nice in that box xD). 

Fig. 13 - Amethyst cluster displaying crystals in darker and more intense violet hues

Fig. 14

Fig. 15 (in cooler lighting)

Fig. 16 - A bigger amethyst cluster with paler hues of violet

Fig. 16.1 (lol) - A rough amethyst pendant

Fig. 16.2 - My two amethyst pendants, polished (top) and rough (bottom)

💎A bit about amethyst: Source 1, Source 2, Source 3, Source 4, Source 5, Source 6

Amethyst is a semiprecious stone and the purple variety of macrocrystalline quartz, typically found in masses of pyramidal short-prismatic crystals (very often in druses), with hues ranging from a very pale lavender and light purple to a rich vivid violet. This gemstone has been used in jewellery and personal adornment for more than 2000 years. Amethyst is most commonly found in the cavities and fractures of igneous rocks, especially basalt flows. 

Fig. 17 - Source

The violet hues of amethyst are a result of irradiation and of the presence of impurities of iron (and, in some cases, other traces of transition metals), which result in complex crystal lattice substitutions: In this process, trace amounts of iron are first incorporated into a growing quartz crystal. After crystallization, silicon is typically substituted by trivalent iron (Fe³⁺) through irradiation caused by gamma rays emitted by radioactive materials within the host rock, thus producing the purple hues of amethyst. 

 

The intensity of this colour can vary from one part of the crystal to another, and so amethyst often shows the phenomenon of colour zoning, with the most intense hues generally found at the crystal terminations. These colour variations are caused by the incorporation of varying amounts of iron during different stages of the crystal growth process, with the darkest purple shades corresponding to the largest amounts of iron incorporated into the growing crystal. Amethyst also shows low pleochroism, changing colours when observed at different angles (typically within the purple chromatic range, for example, from blue-purple to violet).

 

Amethyst infographic from the RBA collection (in Spanish)

 

Fig. 17.1 - Changes in color of amethyst by heat treatment and UV radiation. Note how the deep purple turns to intense yellow and orange-yellow tones, while the lighter purples turn practically white when heated. Source.

When amethyst is heated to reach a temperature of more than 300-400 degrees celsius, the violet hues of amethyst change into yellow, orange and brown, ressembling the naturally rare citrine quartz variety. It is to be noted that most of the 'citrine' that is commonly sold in shops and stalls that offer minerals is treated amethyst, rather than actual natural citrine (see Fig. 17.2). I personally love citrine 🧡 (it will appear in a future post of this series), both the (usually) lighter tones of natural citrine and the deep orange-yellow of 'heated citrine'. There seems to be a distinct distaste for the latter in some parts of the mineralogy community, as I've found. Personally, what mainly irks me is the lack of transparency and the unethical behaviour of pretty much all mineral and 'crystal shops' repeteadly and consistently selling heated amethyst as natural citrine (which is much rarer than both amethyst and smoky quartz, and heat-treated amethyst is of course way more affordable, even if it often doesn't ressemble natural citrine very much). But in and for itself, I quite enjoy the intense orange-yellow of heated amethyst 'citrine'.

Fig. 17.2 - Natural citrine quartz has a more homogeneous lighter yellow hue (or deeper honey, depending in the variety), while heated 'citrine' will feature zones of intense yellow and orange-yellow alongside opaque white bases.

  Lastly, quite rarely found in nature, sometimes amethyst and citrine (or not? see below) are found together in the same crystal, and the resulting bicolour quartz is called ametrine (a combination of 'amethyst' and 'citrine'). However, some studies have shown that amethyst and citrine cannot form in the same environments, and thus 'ametrine' specimens are rather composed of just amethyst with inclusions of iron oxides which create the yellow and orange 'citrine' hues. 'Ametrine' remains its trade name, in any case, so it is typically correct to refer to such specimens as 'ametrine'.

Fig. 17.3 -  Ametrine tumbled stones

Fig. 17.4 -  A beautiful specimen of the rare cactus amethyst variation which I got at a local fair back in May 2023. This specimen include central zones of orange-yellow caused by iron residues being reflected in the crystal sides.

Fig. 17.5 -  Cactus amethyst/ametrine with yellow iron oxide inclusions in the middle.

✨Some interesting history and mythology trivia about amethyst:  

•  The etymology of the name has its origin in Koine Greek αμέθυστος (amethystos) from α- (a-), "not" and μεθύσκω (methysko), "intoxicate". This refers to the belief in Ancient Greece that this stone protected its owner from drunkenness, due to its purple, wine-like colour. Because it was believed that amethyst was an antidote against drunkenness, wine goblets and drinking vessels were often carved from this stone (sorry, but the solution for that is simply not to drink in excess, I'm afraid 😅).
  

• In Ancient Egypt, amethyst was used as a gemstone. Favoured by pharaohs, this stone was carved in the shapes of gods and animals as an amulet to ward against evil. In Medieval Europe, people also believed that amethyst amulets would offer protection in battle. Tibetans also consider this stone to be sacred to the Buddha. 

• Because purple has often been a symbol of royalty in many cultures, amethyst was coveted by royalty in the Middle Ages to decorate regalia. Amethyst was considered as one of the Cardinal gems, the five gemstones considered the most precious (diamond, sapphire, emerald, ruby, amethyst). When large deposits of amethyst were discovered in Brazil since the 18th Century, the more readily available amethyst was then considered a semiprecious stone instead (such is the way of life under capitalism, when it comes to the value attributed to anything 🙃).

• Finally, I also found out that in modern 'crystal healing' (meh xD), amethysts are said to help with insomnia (how tho 🤔 Do they produce melatonin and I've just found out? xD) and that you should put an amethyst stone "underneath your pillow or matress" so that it may help with sleep. And I had this hilarious image of me trying to sleep with one of my large, heavy and pointy amethyst clusters underneath my pillow. That sounds like the antithesis of sleeping better, lol 😅 😂 🤣. Anyway xD
  

5) Blue agate

Fig. 18.1 - Blue agates in my collection: A naturally coloured blue chalcedony/lace blue agate (below, right), alongside an artificially dyed dark blue agate slab, and the specimen from the RBA collection - which is advertised as being a 'naturally coloured blue agate', but I'm pretty sure it's dyed as well, showcasing a very homogeneous dark blue colour that's near identical to the way the agate slab has been synthetically dyed :S

Fig. 18.2 - Blue agate slab from my former existing collection, artificially dyed in a bright cobalt blue.

Fig. 18.3 - Blue agate tumbled stone specimen from the RBA collection.

Fig. 18.4 - Blue agate tumbled stone specimen from the RBA collection. Which also very much looks as if it's a synthetically dyed blue agate, even if it's advertised differently :S.

The blue agate slab in Fig. 18.2 was one of the first ones I got in my first mineral collection when I was little. It's a very bright blue, in a cobalt or peacock blue depending on the light, and is clearly artificially dyed (see below). The tumbled specimen from the RBA collection (Figs. 18.3 and 19.1) has a very similar homogeneous deep cobalt-to-navy blue hue but is described as a "naturally" blue agate from Brazil, "distinguishable from the artifically dyed ones because of the white (and sometimes brown) bands and grooves in it". However, I have to say that I'm pretty sure that this tumbled agate has been artificially dyed as well (see below for a mini rant 😅). I also had a naturally-coloured blue lace agate (blue chalcedony) in my existing collection (see Figs. 18.1 and 18.6-9 below), a polished specimen showing its characteristic banding with various hues of white and grey-blue.

My mineral pendant collection also includes a dyed blue agate (at the top of this pic, polished in a teardrop shape). The rest of the pendants here ( plus a couple of amber and lapis which I forgot to add xD) are, from top to bottom: Red agate (carnelian agate), speckled jasper, dyed blue agate, dyed pink agate geode, fluorite, pink quartz, artificially heated citrine (heat treated amethyst), amethyst, fluorite and dyed howlite (turquenite).

💎A bit about (blue) agate: Source 1,  Source 2, Source 3, Source 4, Source 5, Source 6, Source 7

Fig. 18.5 - Source

 Agate is a translucent fibrous variety of microcrystalline quartz, a banded semiprecious variety of chalcedony (which is also discussed in the jasper section of the third post of this mineralogy series), mainly formed as deposits of hot silica (SiO2) within volcanic and metamorphic rocks. Agate stones can have a wide variety of colours caused by impurities (including brown, white, grey, red, pink, black, yellow and blue), and display characteristic concentric banded patterns which usually include various colours as alternating bands in the pattern (the patterns can also occur as filaments suggestive of moss, resulting in the moss agate varieties). These patterns depend on the impurities present and the conditions under which the mineral solution of silica+impurities is deposited in the rocks. In addition, if the solution cool slowly, quartz macrocrystals can be formed in the central part of the agate stones, while only the concentric microcystalline formations (with no visible crystals) will be be found if the cooling process is faster. 

 

Agate is used as a semiprecious stone depending on its colour(s), interesting patterns, and quality, and has historically been used for jewellery, carvings and decoration for thousands of years. 

✨Some interesting history and STEM trivia about agate:  

• The etymology of the name agate comes from the Ancient Greek Ἀχάτης, the name of the Achates river in present Sicily. It was there that Greek philosopher and naturalist Theophrastus discovered the stone along the riverside, between 400 and 300 BC.  
  

• Agate beads in necklaces were worn by the Indus civilization in the 3rd millenium BC, Bronze Age Minoan culture had agate carvings as well, and the Ancient Greeks used it in jewellery and seal stones.

•  Agate, especially in it blue variety, is held in high esteem in China and India due to its associations with Buddhism, and blue agate was also very popular in the Western Renaissance, being often used to make cameo brooches.
  

• Agate has also quite a lot of industrial and technological uses, due to its hardness and its resistance to chemical attacks. It has been used to create mortars and pestles to mix chemicals, and precision pendulums for laboratory use, for example.  

Blue agate is one of the many agate subvarieties according to colour, mainly composed of blue and white tones in their banding. Because many agates in their natural form actually don't often present striking colours, most of the brightly coloured agate gemstones sold in the market have actually been dyed. The colour in many blue agates is thus most often achieved through dyeing, as is the case of the bright cobalt blue slab in Fig. 18.1, which has been dyed with iron pigments to achieve that bright blue shade (which is also the case of the similarly bright cobalt blue specimen from the RBA collection, as I'll comment on below 😬).  

Naturally ocurring blue agates do exist, such as the "Holley blue agate" and the blue lace agate (also referred to as blue chalcedony, see Fig. 18.1 and Figs. 18.6-9). In blue lace agates, layers of blue chalcedony are interlayered with colourless or white chalcedony and quartz. In contrast to the brighter and darker hues of the artifically dyed agates (most brightly coloured agates are dyed, as stated above), the blue tones of the holley and blue lace agates tend to be much lighter, combining various hues of greyish-blue with white in their characteristic "lacy" banding patterns:

Fig. 18.6 - Lace blue agates (blue chalcedony) in my former existing collection.

Fig. 18.7 - A lace blue agate (blue chalcedony) in my former existing collection.

Fig. 18.8 - A lace blue agate (blue chalcedony) in my former existing collection.

Fig. 18.9 - A lace blue agate (blue chalcedony) in my former existing collection.

So, is the specimen from the RBA collection artificially dyed in spite of it being advertised as a naturally-colour blue agate? Yes, the blue agate from the collection is also artificially dyed. And well, this reflects poorly on the ethical transparency of National Geographic and the RBA collection,  I have to say 😕, as it's clearly advertised as being a 'naturally coloured blue agate', even going as far as citing in the descriptive text how many of these agates are dyed and how difficult it can sometimes be to distinguish between them 🙃 (see Fig. 19.2 below). Later collections such as 'Minerales de la Tierra' ('Minerals of the Earth') have also done this. I would typically have zero problems about a mineral collection including an artificially dyed specimen (even though I personally much prefer the naturally coloured agates and the inclusion of a blue lace agate in the collection, instead of a brightly dyed agate, would have perhaps made more sense. Later int he collection we do get a 'blue chalcedony', an actual lace blue agate, phew xD). But what is problematic is advertising a mineral as 'naturally coloured' when it's blatant that it has been most definitely dyed :S.

Fig 19.1 - Blue agate tumbled stone from the RBA collection against the light. The blue colour looks too homogeneous and artificial (and dark) to be natural.

As we can see in Figs. 18.4-5, this blue agate showcases a very homogeneous dark blue colour that's near identical to the way the agate slab in Fig. 18.2 has been dyed, and when looking at it against the light (Fig. 19.1) you can clearly see that, instead of having white and brown banding as advertised, everything has a blue hue that looks very artificial :S This video also shows how these 'blue' agates are dyed by rubbing the specimen with alcohol and seeing how the paint comes off immediately. This specimen also doesn't show any white or brown banding similar to the promotional pictures, which, according to the infographic in Fig. 19.2, is 'what helps identify a naturally coloured blue agate from a synthetically dyed one' (banding patterns which we see in the blue lace agate above and not in this one). The specimen that I got may even be a clear quartz that has been dyed, not even an agate, as the lack of any kind of banding is suspicious (but I'm not 100% sure on this, it might be a regular agate (chalcedony) that's been dyed). And even though it does show some small brown patches against the light, this tumbled stone still looks near identical to synthetically dyed blue agates such as these below, down to the blue hue and the white scratches/grooves on the surface. So yeah, it's 100% dyed.

Source (crystal healing topics which I don't condone, though, but at least these are described as 'synthetically dyed blue agates'!

Fig. 19.2 - Infographic on the 'naturally-coloured' blue agate in the RBA collection (in Spanish) - including some jarring info about the 'crystal healing' 'uses' of blue agate at complete face value 😬🙃.

 

And following my rant on 'crystal healing' above in this post, this is the first infographic that I've read that also includes content about this pseudotherapy, in a way that seems to be worded at complete face value - which I find both jarring and again, kinda unethical 😬. No, a blue agate, artificially dyed or no, will not cure your fever or your sore throat, lol 😅. If this is a mineralogy and gemology collection, how about keeping the infographics and the divulgative content of each installment strictly scientific? This is not to say that mythology, religion, history or superstition related to a mineral or gem might not come into play in the text (as these topics sometimes do in my trivia here), but preferably worded in a way that does not legitimize something that has literally zero scientific evidence as fact 🙃. My experience with scientific material from National Geographic is also touch and go in regards to Astrophysics (especially when it comes to cosmology and the Big Bang 😅), but so far the errors that I have been able to encounter in this collection have been reasonably minimal (and often also associated to cosmology or nucleosynthesis, Astrophysics topics, for some reason 😅), and I'd still say that the overall balance of this collection is pretty good. But yeah, this installment included more than one problematic thing :S.

 

6) Fluorite: 

Fig. 20.1 - My fluorite specimens as of January 2024, including 4 rough specimens and two tumbled fluorites.

Fig. 20.2 - Fluorite specimen from the RBA collection (left) alongside the first fluorite in my collection (right). Both are green as their main colour, the left one showing banding and colour zoning in purple and blue, and the right one showing some zoning in light pink.

 

Fig. 20.3 - Pale green fluorite with pink zoning (artificial light), the first fluorite in my collection.

Fig. 20.4 - Pale green fluorite with pink zonin (direct sunlight).

Fig. 20.5 -  A rough green fluorite pendant.

Fig. 20.6 -  A rough green fluorite pendant, similar to the specimen in Figs. 20.3-4. This one is mostly all green , however, with only the slightest tinge of pink against the light. 

Fig. 20.7 -  Green fluorite from the RBA collection. The depth and shade of the greens, blues and purples change rather drastically with the lighting and depending on whether photos use flash or not.

Fig. 20.8 -  Green fluorite from the RBA collection (artificial light), a light green against the light with more prominent zoning in purples, blues and yellows.

Fig. 20.9 -  Fluorite from the RBA collection, in direct sunlight, showcasing a lovely array of colour zoning.

Fig. 20.10 -  Fluorite from the RBA collection, in direct sunlight.

Fig. 20.11 -  Green and purple fluorites: A small tumbled stone from a local fair (left), and the specimen from the RBA collection (right). The left one features colour banding in greens and purples, while the  specimen on the right displays less defined zoning in blue, deep purple and yellow.

Fig. 20.12 -  A small tumbled stone from a local fair (below), and the specimen from the RBA collection (above).

Fig. 20.13 -  A small tumbled fluorite from a local fair, displaying a very defined banding pattern with various shades of green and purple. 

 

 

Fig. 20.14 -  A fluorite pendant from a local fair which shows an striking array of green, purple and clue colour banding against the light.

Fig. 20.15 -  A fluorite pendant from a local fair which shows an striking array of green, purple and clue colour banding against the light.

 

Before 2023, in my existing collection I only had one specimen of fluorite from Mexico, a small pale green one with some subtle pink zoning (in Figs. 20.2-4). This specimen is quite similar to a rough green fluorite pendant that I got in October 2023 (Figs. 20.5-6), although it's mostly all pale green with the slightest tinge of pink in one side when seen against the light. The specimen from the RBA collection (Figs. 20.2, 20.7-10, and 20.11-12) is from China, and it is a quite beautiful one, with colour hues that change depending on the angle and the lighting, featuring an intense emerald green as its main colour (it looks a similar light green to the others against the light, and a deeper vivid green in most lightings), and a deep purple section. This piece also includes some sky blue zoning, and a bit of yellow as well.

 

   This lovely variety of hues is also predominant in the fluorite pendant that I got in a September 2023 local fair (Figs. 20.11-13), which looks medium-to-dark green with a dark purple zone but also shows an striking banded array of greens, purples and light blue against the light. I also got a small tumbled fluorite as a gift at another local fair back in May 2023 (Figs. 20.14-15), displaying the most defined banding pattern out of all the fluorite specimens in my collection, in several hues of green and purple. 

 

   In December 2023, I got another fluorite in massive habit (Figs. 20.17-21), with a translucent light green as its main colour, plus a couple of purple zones (especially a larger zone at one tip of the piece), and some cyan blue zoning appearing when looking at it against the light. The banding is not so prominent in this piece in contrast to the tumbled fluorites, but you can also see some purple and cyan banding patterns against the light. The characteristic vitreous luster of fluorite also creates a subtle iridescent effect on the surface for this particular piece (a result of light refracting through layers of crystallization, as seen, for ex., in Fig. 20.18 and the videos below), and it's very pretty to look at! 

 

Fig. 20.17 - The largest fluorite in my collection so far, mostly green with a distinct purple zone.

 

Fig. 20.18 - This specimen of fluorite showcases a lovely vitreous luster, and also shows some iridescence on the surface at some angles, as a result of the scattering of the incident light by the translucent crystal layers.

 

Fig. 20.19 - Green and purple fluorite against direct evening sunlight (featuring a rainbow lens flare on the right).

Fig. 20.20 - Green and purple fluorite against direct evening sunlight. The subtle cyan zoning in this piece is more noticeable here, close to the purple banding and zoning at the top.

Fig. 20.21 - Green and purple fluorite against direct evening sunlight.

Fig. 21. Source.

💎A bit about fluorite: Source 1,  Source 2, Source 3, Source 4, Source 5, Source 6

 Fluorite (also known as Fluorspar) is the mineral form of calcium fluoride (CaF₂). Part of the halide minerals, fluorite is very common in many parts of the world, often occurring in rocks as vein fillings as a result of hydrothermal processes, and also found in fractures and cavities of dolomites and limestones. Fluorite presents well-formed crystals, usually cubic, and it can also occur in several other habits, such as massive, nodular, granular or boytroidal.

Although pure fluorite is transparent and colourless (both in visible and ultraviolet light), fluorite is also allochromatic, as impurities and exposure to radiation can tint it and make it a very colourful mineral. Thus, fluorite can come in a wide variety of colours with a transparent-to-traslucent appearance, from purple, blue, green and yellow (the most common), to pink, red, brown, white and black. Colour banding and zoning can also appear. 

Fluorite has multiple uses in the chemical, ceramic and metallurgical areas, and particularly beautiful specimens regarding their colour and diaphaneity can also be cut into gems (although their relatively low hardness of 4 in the Mohs scale makes this more difficult than in the case of other gemstones) and used for ornamental purposes.

Fig. 22. Fluorite infographic from the RBA collection (in Spanish).

✨Some interesting history and STEM trivia about fluorite:  

•  The etymology of the word is derived from the Latin fluere ("to flow"), and this is related to the low melting point of the mineral. Fluorite has been historically often used as a flux (chemical cleaning or flowing agent) in iron smelting (applying heat to ore) in order to decrease the viscosity of slag (by-product of smelting ores and metals). 

• Fluorite is also called fluorospar, a name coined in 1530 by Georgius Agricola, a German scientist specialized in metallurgy and mining.  This name is a neo-Latinization of German Flussspat, derived from Fluss ("stream, river") and Spat (a non-metallic mineral). 

• Fluorite also gave its name to its constitutive element, fluorine (F), and also to the phenomenon of fluorescence, discovered in fluorites by George Gabriel Stokes in 1852. Many samples of fluorite exhibit fluorescence, glowing a a blue-violet or yellow colour under short-wave and long-wave ultraviolet light. This phenomenon is due to certain impurities in the crystal, trace amounts of yttrium (causing the yellow glow), europium (causing the violet glow), samarium, or other elements substitute for calcium in the fluorite mineral structure.

• Fluorite has multiple uses industrially: It is used as a flux for smelting, as mentioned above, as well as being a source of fluorine and hydrofluoric acid. This mineral is used in the production of some types of glass and enamel, and transparent fluorite lenses, which exhibit low dispersion and thus less chromatic aberrations, are extensively used in optical instrumentation, especially in telescopes and microscopes. Fluorite optics are also used in the far-ultraviolet and mid-infrared ranges, where conventional lenses are too opaque for use.    

And to finish, a couple of videos of my fluorites:

7)  Celestine: 

Fig. 23 - The large celestine cluster from the ren faire (left), and the medium-sized cluster from the RBA collection. Both feature beautiful crystals and the typical grey-blue tones.

Fig. 24 - The large celestine cluster from the ren faire (left), and the medium-sized cluster from the RBA collection.

Before getting the RBA collection specimen (a medium-small cluster from Madagascar, Figs. 23, 24 and 26), I was lucky to get a gorgeous celestine cluster at a local ren faire in December 2022 😃✨💎 (Figs. 23, 24 and 25.1-4). To no one's surprise, the stall was full of pseudoscientific 'crystal healing' mumbo-jumbo, including the baffling case of a certain tumbled gemstone (I don't recall which it was) which supposedly had the property of 'resetting the ADN'. LOL 🤨🤣  But if that's the price I have to pay to get this gorgeous celestine cluster with its beautiful clear greyish-blue hue 💙, I guess I'll take it xD:

Fig 25.1 - The large celestine cluster from the ren faire

Fig 25.2 - The large celestine cluster from the ren faire

Fig 25.3 - The large celestine cluster from the ren faire

 

Fig 25.4 - The large celestine cluster from the ren faire

Fig 25.5 - The large celestine cluster from the ren faire

Fig 26 - The smaller celestine cluster from the RBA collection

 

Also, a couple of videos:

💎A bit about celestine: Source 1, Source 2, Source 3, Source 4, Source 5, Source 6

Fig. 26. Source.

Celestine (also known as Celestite) is a mineral that consists of strontium sulfate (SrSO4). Celestine is so named for its most famous hue, a celestial clear pale grey-blue (other colours for celestine - all of them created by impurities, as pure celestine is colourless - include rarer shades of red, orange, yellow and green). This mineral is fragile and hard to cut, and so it is very seldom used in jewellery, being found mostly in its rough geode or cluster form. Celestine is instead esteemed among collectors for its beautiful and well-formed (di)pyramidal crystals with their distinctive blue colour.

✨Some interesting trivia about celestine:  

•  The etymology of the word is derived from the Latin caelestis "celestial", from caelum "sky, heaven", and refers to its grey-blue sky-blue colour. The mineral started to be called "Celestite" in 1798.
  

• Celestine is the primary source of strontium, which mixed into a metal salt is used to created red-coloured fireworks (not a fan, but cool chemistry fact, I guess 😅).

• Celestine is a luminescent mineral, glowing bluish-white when exposed both to heat (thermoluminescence) and ultraviolet light (fluorescence).
  

• The New Age, 'metaphysical' and 'crystal healing' pseudoscientific world claims that Celestine can be used as a focus for meditation and mindfulness, and its "high vibrations" help with spiritual development, aura cleansing, flushing out "toxins", astral dreaming, and angelic communication (well, maybe Aziraphale fashioned a vintage telephone out of it in Good Omens 😅 😂). You supposedly "charge" it in moonlight. All of this is of course scientifically unfounded.

Even actual angels (and demons) seem to prefer to use an actual phone as a first option 😅 😂

Fig 28. Celestine infographic from the RBA collection (in Spanish). Curiously, the advertised celestine in this number from the collection lacks the typical grey-blue colour of these crystals, instead showcasing the colourless/white variety.

-Finally, here are some infographics from the collection (in Spanish) about all the minerals in this post: gold, quartz, rose quartz, Tiger's eye, amethyst, blue agate, fluorite and celestine (click on the pics or open in new tab for larger pics!):

 

So that's it for today! On the next minerals post: Fuchsite, rhodonite, quartz geodes, pyrite and galena 😃💎