Expanding my mineral collection III: Red jasper, Iceland spar, obsidian, azurite, and chalcanthite

Fig.1 - Red jasper, Iceland spar and obsidian (top row); desert rose (this one is for the next post xD) and azurite (bottom row)

Third post in my new mineralogy series incoming, talking about my mineral collection ✨💎! 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. What really gave me the final nudge to rediscover mineralogy as an active hobby 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. 2 - My mineral collection as of May 2022, featuring the fuchsite, rhodonite, quartz geode, galena (see the second post in this series) and red jasper from the RBA collection ✨💎

Fig. 3 - My mineral collection as of June 2022, featuring the fuchsite, rhodonite, quartz geode, galena (see the second post in this series), red jasper, Iceland spar and obsidian from the RBA collection ✨💎

In this third post we're gonna keep following the order of the RBA collection, and talk about four minerals, up to the first 16 minerals in the collection: red jasper, Iceland spar, obsidian, azurite and copper sulfate/chalcanthite 😃💎. As I explained in more detail in post 1, in this series I will show the specimens from the RBA collection alongside the ones in my existing collection before collecting the kiosc numbers, and also any pieces from new hauls.

13) Red Jasper:

Fig. 4.1 - All of my red jasper specimens in my collection: Most of them are tumbled stones - RBA collection (above, right), and two others from my former existing collection (front, and left, above); alongside a red jasper in its natural rough form (in the middle).

Fig. 4.2 - All of my red jasper specimens in my collection: Most of them are tumbled stones - RBA collection (above, left), and two others from my former existing collection (above, right, and below, right); alongside a red jasper in its natural rough form.

Fig. 5 - The red jasper tumbled stone from the RBA collection

Fig. 6 - Red jasper specimen in its rough form. Its conchoidal fracture, with smooth and curved edges, can be easily appreciated here.

 In my existing collection, I had three specimens of red jasper (Fig. 4), two tumbled stones and a rough red jasper specimen. The boxed ones (both specimens originating from Brazil) are part of a couple of collections from the science shop of the former CosmoCaixa museum. The RBA collection specimen (also from Brazil) is another tumbled stone, the largest out the three.

💎A bit about red jasper: Source 1,  Source 2,  Source 3, Source 4, Source 5, Source 6, Source 7, Source 8

Fig. 7 -  Chaldedony infographic (source)

Jasper is a variety of chalcedony, so let's introduce that mineral first, and then focus on (red) jasper per se:

Chalcedony is a microcrystalline compact form of silica composed of very fine intergrowths of  quartz (SiO₂, also see post 1) alongside small amounts (between 1% and 20%) of the silica mineral moganite. Chalcedony appears in numerous varieties, which are mainly classified as agates and jaspers (see below), with various lusters (from waxy, to vitreous and silky), and displaying a wide range of colours. Microcrystalline quartz in its pure form is semitransparent, and the different colours and levels of diaphaneity (from translucent to opaque) tend to appear due to the addition of varying amounts of impurities. 

 The most common hues displayed by chalcedony are white, grey, brown (see all the banded agates in post 2), and greyish-blue (for ex., the lace-blue agate in post 1), but we can also find chalcedony specimens in reds and oranges (as in the case of red jasper, carnelian or red onyx, deriving their colour from iron oxides), greens (for ex., chrysoprase and green jasper, deriving their hues from nickel impurities), and black (as in the case of black onyx, which is rare in nature and usually dyed). Many chalcedony specimens (for example, numerous banded agates), are artificially dyed or heated to achieve enhanced and/or brighter colours that are not to be found naturally (see the dyed blue agates in post 1 vs the naturally coloured agates in post 2).

 ✨Some interesting historical trivia about chalcedony:   

• The word "chalcedony" comes from the Latin chalcedonius, probably derived from the Turkish town of Khalkedon (Chalcedon) in the Asia Minor of Ancient Times. Pliny the Elder mentioned the name in his Naturalis Historia to name a translucent variety of jasper.

•  Uses: Chalcedony being a very hard and durable material, breaking with a conchoidal fracture with smooth, curved and sharp surfaces, it has been used for thousands of years to manufacture tools and weapons (in these contexts, usually under the name of 'flint'). With its colourful varieties and its luster and ability to be brightly polished and tumbled, chalcedony has also been historically used for jewellery and ornaments, and in the Bronze Age this mineral was already in ample use in the Mediterranean and Central Asian regions (featuring seals, beads, rings and cameos).
  

Fig. 8 - Jasper infographic (source)

 

Both jasper and agate are varieties of chalcedony, and the main difference between them is their diaphaneity: Jasper is opaque while agate is translucent to semi-transparent (typically with banded patterns). In the first post of this series, agate was described as forming in the cavities of igneous and metamorphic rocks as deposits of hot silica. Jasper, on the other hand, often forms in soft sediments when silica precipitates, cementing them into a solid mass. Jaspers can also form from silica precipitation when volcanic ash is cemented into a solid material, and sometimes this process is so violent that the sediments and ash dissolve and then recrystallize into microcrystalline quartz. These fine materials (sediments and/or volcanic particles) are what give jasper its opacity and its varying colours.

 

 'Flint', 'chert' and 'jasper' are names used to describe opaque varieties of chalcedony, with the usage of 'flint' being favoured by historians and archaeologists (especially when referring to human-made artifacts and weapons with this material), 'chert' by geologists (when referring to this material as a sedimentary rock unit forming in extensive bedded deposits), and 'jasper' being a more gemological term: Jasper would thus be described as opaque microcrystalline quartz (chalcedony) in attractive colours that can be carved, cut, tumbled and polished as a gem, usually in the shape of tumbled stones, cabochons and spheres.

 

Jasper generally appears with red, yellow, brown, green and (rarely) blue colours, due to the presence of different impurities in the silica (the higher level of  impurity inclusions from different non-chalcedony materials being the reason why this variety of chalcedony is opaque). The rich and homogeneous red hues of red jasper, the main variety of jasper that concerns us here, are a result of iron oxide inclusions. 

✨Some interesting STEM trivia about red jasper:  

• The word "jasper" means "spotted or speckled stone" and derives from the Old French jaspre (a variant of Anglo-Norman jaspe), and Latin iaspidem (nom. iaspis), from Ancient Greek  ἴασπις (iaspis). This Greek work, in turn, comes from a Semitic language - For comparison, we have Hebrew ישפה (yashpeh) or Akkadian yashupu. The Persian word for the mineral jasper is also yashp (یَشم). 

• Uses: With its name being traced back in Persian, Assyrian, Hebrew, Arabic, Greek and Latin, since Ancient times jasper has been polished and used as a gem to make jewellery and ornaments (from seals, to cameos, beads, rings or vases). For example, jasper seals dating back to c. 1800 BC in Minoan Crete have been found in Knossos, and in Ancient Egypt amulets made out of red jasper were common, as this gem was revered as a sacred stone linked to the goddess Isis and associated with fertility and protection (see the first post for some context on the modern 'crystal healing' as a pseudotherapy and pseudoscience). Many mentions of jasper in antiquity actually refer to the green variant rather than the red, compared to emerald and other green stones (it might have also been akin to the green chalcedony variety now named chrysoprase).

Fig. 9 - Red jasper infographic from the RBA collection (in Spanish)

 

14) Iceland spar:

Fig. 10 - The Iceland spar specimen from the RBA collection

 This was my first Iceland spar my existing collection (Fig. 10), and I was really excited to get this one because of the birefringence property of this clear calcite crystal 😃 (see below). This is a rhombohedral specimen from Mexico, displaying perfect cleavage, and also easily scratched, with a white streak that minimizes its birefringence properties, so handled with care it must!

Fig. 11 - Calcite infographic (Source)

💎A bit about Iceland spar and birefringence: Source 1,  Source 2,  Source 3, Source 4, Source 5

Iceland spar (also known as Iceland crystal and optical calcite), is a transparent variety of calcite (crystallized calcium carbonate, CaCO₃), an abundant rock-forming mineral found worldwide in igneous, metamorphic and sedimentary rocks alike. Iceland spar is so named for having originally been brought from Iceland, and is remarkable for its birefringence, an optical property where the refractive index of the crystal changes depending on the polarization and the direction of propagation of the incident light.

Birefringence is responsible for the phenomenon of double refraction, by which an incident ray of light is divided into two rays of perpendicular polarization that are directed at slightly different angles - Causing objects to appear doubled when seen through the birefringent crystal. 

Fig, 12 - Example of birefringence (Source). Here, the optic axis along the surface is perpendicular to plane of incidence. Incoming light in the s polarization (perpendicular to plane of incidence, thus "parallel polarization" to optic axis) sees a greater refractive index than light in the p polarization ("perpendicular polarization" to optic axis)

Fig. 13 - Birefringence (Source)

As a result of these properties, Iceland spar has been widely used historically to study double refraction and to demonstrate the polarization of light, with Danish scientist Rasmus Bartholin first describing double refraction in 1669 with the aid of calcite. In the 1820s, Augustin-Jean Fresnel described this phenomenon in terms of polarization, studying the nature of light as a wave, as per Christiaan Huygens's wave theory of light (1690). Some other scientists who studied the birefringent properties of Iceland spar include William Nicol, who invented the first polarizing prism in 1828 (the Nicol prism) by making use of this clear calcite variety; and Sir George Stokes, who studied the double refraction of Iceland spar in 1862.

 The short video below shows the birefringent properties of my Iceland spar specimen. When placing the mineral over the page, the words appear twice, and if we rotate the rhombohedral specimen around itself, we will see that one of the texts doesn't move, while the duplicated one rotates in a circle around the former:

 ✨Some interesting historical and STEM trivia about Iceland spar:   

• One alternate name of Iceland spar is 'Iceland crystal', and in Icelandic it's named silfurberg  "silver-rock".

Fig. 14 - Iceland spar used as sunstone (Source)

•  The Viking sunstone?: Iceland spar could be a probable candidate for the Old Norse sólarsteinn "sunstone" mineral mentioned in 13th-14th Medieval Icelandic texts such as Rauðúlfs þáttr, where this sunstone is described as being used to locate the Sun in an overcast or snowy sky, by holding up up and observing where the stone emitted, reflected or transmitted light:

 

Fig. 15 - Use of sunstones for navigation

 

"Veður var þykkt og drífanda sem Sigurður hafði sagt. Þá lét konungur kalla til sín Sigurð og Dag. Síðan lét konungur sjá út og sá hvergi himin skýlausan. Þá bað hann Sigurð segja hvar sól mundi þá komin. Hann kvað glöggt á. Þá lét konungur taka sólarstein og hélt upp og sá hann hvar geislaði úr steininum og markaði svo beint til sem Sigurður hafði sagt."

 

"The weather was thick and snowy as Sigurður had predicted. Then the king summoned Sigurður and Dagur (Rauðúlfur's sons) to him. The king made people look out and they could nowhere see a clear sky. Then he asked Sigurður to tell where the sun was at that time. He gave a clear assertion. Then the king made them fetch the solar stone and held it up and saw where light radiated from the stone and thus directly verified Sigurður's prediction" (translation by Thorsteinn Vilhjalmsson, Source).

   Viking seafarers could have been making use of the light-polarizing properties of Iceland spar for navigational purposes in this way. The polarization of sunlight in the Arctic latitudes can be indeed detected with a mineral such as Iceland spar (or other minerals with similar light-polarizing properties, such as iolite, called 'Vikings' compass'), and the azimuth of the Sun can be consequently identified with the naked eye to within a few degrees in cloudy skies and when the Sun is just below the horizon.  

 

Fig. 16 - In the series Vikings (2013-2020), Ragnar Lothbrok uses what looks like a large specimen of Iceland spar as a sunstone to help with navigation in his seafaring (and plunder).

As these videos below illustrate, one possible way that Scandinavian seafarers could have used the sunstone as a navigational tool consists in placing a dot on top of the crystal with pine tar or charcoal, and then pointing the stone at the brightest part of the horizon. Looking up from the bottom of the crystal, the navigator would see two dots appearing, refracted through the stone due to birefringence. The direction of the Sun could be found by moving the crystal along the horizon until these two points had the same brightness. In this position, the front the crystal would be pointing towards the Sun:

 

 

In addition to Viking seafarers, a sunstone was additionally found in a 16th century Elizabethan shipwreck, which may point to the continued use of such stones as navigational devices even when the magnetic compass was already well in use. And beyond their use in nautical navegation, sunstones are also mentioned in 14th-15th century Ireland and Germany as part of churches and monasteries, which were probably using these polarizing crystals in conjuction with known landmarks as a sundial to keep track of time, particularly at high latitudes with limited hours of sunlight and extended periods of twilight, as well as in mountain areas and in frequent overcast weather conditions.

Fig. 17 -  Iceland spar infographic from the RBA collection (in Spanish)

15) Obsidian:

Fig. 18.1 - Obsidian specimens in my collection, including raw and tumbled pieces of snowflake obsidian, mahogany obsidian and regular black obsidian.

Fig. 18.2 - The snowflake obsidian specimens in my collection: All of them tumbled stones, except for the specimen from the RBA collection (above, left), which is in its rough unpolished form.

Fig. 19.1 - Rough snowflake obsidian specimen from the RBA collection. Its conchoidal fracture, with smooth and curved edges, can be easily appreciated here.

Fig. 19.2 - Snowflake obsidian tumbled stones.

Fig. 20 - Rough black obsidian from a set including various Chilean minerals.

Fig. 21.1 - Raw black obsidian pieces from the RBA collection. Left is a 'mahogany obsidian', only with only part of the piece tinted reddish-brown by iron impurities. 

Fig. 21.2 - Raw black obsidian from the RBA collection.

Fig. 21.3 - Raw black obsidian pieces from the RBA collection. Left is a 'mahogany obsidian', only with only a tiny part of the piece tinted reddish-brown by iron impurities.

   Most of the obsidian specimens I had in my existing collection are tumbled, featuring four tumbled stones of snowflake obsidian (Figs. 18.1-2 and 19.2) of varying sizes and differing abundance of their characteristic cristobalite spherulite inclusions (see below). I also had some small pure black obsidian in the rough, from a Chilean mineral set (Fig. 20). As for the new pieces, the RBA collection includes not only one, but three obsidian specimens: The first one is a rough obsidian of the snowflake variety from USA (Figs. 18.1-2 and 19.1), followed, near the end of the collection, by two rough black obsidian pieces from México (in Figs. 18.1 and 21.1-3). Both of them showcase the characteristic conchoidal fracture of this volcanic glass variety, with visually striking smooth (and very shiny) curved surfaces, as well as the typical concentric undulations ressembling lines of growth in a shell (see, for ex., Fig. 21.2).

   One of these was sold as a 'mahogany obsidian' (Figs. 18.1, 21.1 and 21.3), a variety which includes varying degrees of mahogany tones due to iron inclusions (see below). However, this one falls under the "subpar (and kinda dodgy)" category in this collection, given that the piece I got can hardly be called a 'mahogany obsidian', sporting only a minimal amount of reddish-brown tones. It is much more a regular black obsidian than a mahogany one. To the surprise of no one, the cover of the associated booklet also showcased a specimen of mahogany obsidian resplendent in its abundant bright reddish-brown tones, lol 🙃. So, the end result in this case was to make collectors buy two near identical specimens of regular black obsidian in its raw form. Ah well.

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

Fig. 22 - Obsidian infographic (Source)

  Obsidian is a naturally occurring volcanic glass with a smooth texture and a glassy shine which is amorphous, hard and brittle, with a characteristic conchoidal fracture. Found worldwide in areas of volcanic activity, it is formed when silica-rich lava flows with high viscosity cool so rapidly that atoms are unable to form a crystalline structure, instantly solidifying as an amorphous glass. Sometimes also known as a 'mineraloid', obsidian is thus an igneous rock and not a true mineral, both because of its lack of crystalline structure and its very variable composition (although typically similar to that of the silica-rich igneous rock rhyolite). Most commonly an extrusive rock (solidifying above the surface of the Earth), obsidian is produced from felsic lava, rich in elements such as silica, oxygen, aluminium, pottasium and sodium.

    The most common colour for pure obsidian is deep black, sometimes also showcasing brown, reddish or green tones, and very rarely blue, yellow and orange hues. All of these colours are caused by trace elements and inclusions, with iron (via the presence of hematite, for example) and other transition elements giving it the characteristic dark brown to black hues. For example, the 'mahogany obsidian' variety features reddish-brown, mahogany tones due to iron (hematite) inclusions (see Figs. 21.1, 21.3 and 23.1-2). 

Fig. 23.1 A Mahogany obsidian.

Fig. 23.2 - One of the tumbled snowflake obsidians also sports small mahogany-toned patches due to iron inclusions.

   With the passage of time, obsidian, a chemically unstable glass, begins to crystallize at a non-uniform rate. The crystallization process forms radial clusters of white and grey cristobalite spherulites within the volcanic glass (cristobalite has the same chemical formula as quartz, SiO₂, but a distinct crystal structure), producing a snowflake pattern and creating specimens which are fittingly known as 'snowflake obsidian' (see Figs. 18.1-2 and 19.1-2). More rarely, some obsidian specimens can showcase a golden, silver or rainbow iridescent sheen caused by the light being reflected off gas bubbles resulting from the lava flow or minute inclusions of mineral crystals. These varieties are known as 'golden/gold sheen obsidian' (with a golden sheen), 'silver/silver sheen obsidian' (with a silver sheen), and 'fire/rainbow obsidian' (with colourful, iridescent rainbow patterns) (see Fig. 23.3). 

Fig. 23.3 - Golden/gold sheen obsidian (left) and rainbow obsidian (right, source)

 ✨Some interesting historical and STEM trivia about obsidian:   

•  In in his Natural History, Roman writer Pliny the Elder included mentions of a volcanic glass discovered in Ethiopia by a Roman explorer called Obsidius, thus the name 'obsidian' (lapis obsidianus, "stone of Obsidius") 

• Obsidian in history: Because its breaks with a characteristic conchoidal fracture, creating curved and sharp edges, obsidian has been used by numerous cultures since the Stone Age (c. 700,000 BC) to manufacture cutting tools, from knives, to spear points and arrowheads. Early mirrors were also made out of polished obsidian in Ancient times, because of its high luster and reflective properties, and it has been consistently carved into jewellery and many artifacts and decorative objects (figurines, sculptures, masks,...). Obsidian was considered a highly valued commodity in Ancient times, with many artifacts and tools travelling far and wide thanks to widespread trading:
   
  Obsidian objects had become common by the Upper Paleolithic and have been found in many Neolithic cultures in Central Europe, and in Turkey dating to the 5th millennium BC. Ancient Egyptians imported obsidian from the eastern Mediterranean regions. Minoan Crete, as well as the areas of modern Hungary and Slovakia, were some of the main sources in Europe. The Japanese areas of volcanic activity were another focal point of obsidian tool making. In America, the Aztec culture used obsidian in a very sophisticated way, and Native North American peoples traded it in a widespread way. Obsidian was also widely used throughout Oceania since at least 1000 BC, with Pacific cultures engaging in long distance trading, and many tools showing complex production techniques that would indicate the association of the use of this volcanic glass with high status.
  

• Modern uses: Thin blades of obsidian have been used to create precision scalpels in the field of modern surgery. While obsidian blades can be thinner and sharper than any steel blade, their major disadvantage is their brittleness, thus limiting their use to specialized uses where this would not be a concern. One of the main industrial uses of obsidian is to manufacture glass wool, used in building construction for thermal and accoustic insulation. Several variations of obsidian, such as snowflake obsidian, are also considered as a semiprecious stone, and used for ornamental purposes, cut into beads, cabochons and tumbled stones.

• Apache tears:  This is the name that has been given to rounded pebbles of black obsidian, or 'obsidianites'. Mainly found in Arizona and Nevada, the name calls back to a legend of the Native American Apache tribe, recounting  a battle between 75 Apaches and the US Cavalry in the 1870s in a mountain in what is now Arizona. Rather than face defeat, the outnumbered Apache warriors preferred to jump their horses off the mountain. Upon hearing the news (and probably awaiting slavery or death themselves), the wives and families of the fallen warriors wept, their tears turning into dark pebbles upon hitting the ground 😕.

Fig. 24 - Obsidian infographic from the RBA collection (in Spanish)

16) Azurite:

Fig. 25 - Large azurite and malachite specimen over a goethite matrix plate, from a local fair. It is absolutely gorgeous, and easily one of my top 5 fave specimens in my collection 😍

Fig. 26 - Two azurite specimens from the RBA collection.

 

Fig. 27 - The first azurite specimen I got from the RBA collection, featuring small azurite crystals (as well as some green malachite crystals) over a goethite matrix.

Fig. 28 - The second azurite specimen I got from the RBA collection, with larger patches of azurite over what looks like a goethite rock piece.

Fig. 29 - Another shot of the large specimen from the local fair. Its front is nearly completely covered by the azurite and malachite crystals.

Fig. 30 - Another shot of the large azurite and malachite specimen from the local fair.

Fig. 31 - The back of the large specimen. Contrasting with the front, the back and sides feature small crystals of both azurite and malachite dispersed on the goethite matrix plate. It's very much like the small RBA specimen in Fig. 27, but considerably larger.

  Azurite is one of my favourite minerals, mostly because of its deep blue colour 💙. I didn't have any azurite specimens in my former collection, and all of a sudden I got three of them this year, so yay 😃 xD. Two of them are from the RBA collection (Figs. 26-28, both of them from Morocco), and then I found the most gorgeous large azurite and malachite specimen at a local fair this past Spring (Figs. 25 and 29-31). I was a bit disillusioned with the first specimen from the National Geographic collection (Fig. 27). Its small azurite and malachite crystals, embedded in what looks like a matrix plate of goethite, an iron oxyde-hydroxide mineral typically associated with azurite (also see gossan rock), are undeniably beautiful, but I was expecting a bit more of a presence of azurite, so to speak 😅, and so I got the same number from the collection when it started selling in kioscs again from the top (I've since done this with a couple of others because I wasn't satisfied with the specimen I already had and wanted one more....perfectionist, me? Hoarder-collector, me? Nope 😅 xD). The second specimen I got from the same collection (the renewed round of it, that is) showcased azurite patches that were a little larger (Fig. 28), something which I was initially going for. 

 

   I still wanted to find a larger azurite(+malachite) specimen sometime, and then I visited a local Spring fair which had a minerals stall and voilà, I fell in love with a large (and surprisingly affordable!) specimen, featuring extensive patches of mainly azurite but also malachite (love the combination!) on a large matrix plate of goethite. It's like the amped up (and utterly gorgeous) edition of both RBA specimens, featuring both the more homogeneous patches of azurite and malachite patinas on the front (Figs. 25 and 29-30), and the small crystals strewn upon the rock in the sides and back (Fig. 31). I found this specimen quite by chance, and it has easily become one of my top faves in my whole collection 😍💎.

Fig. 32 - Azurite infographic (Source)

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

  Azurite is a soft copper carbonate hydroxide mineral (Cu₃(CO₃)₂(OH)₂) formed as a secondary mineral by the weathering of copper ore deposits by carbon-dioxide-laden waters, often occurring in fractures and cavities of subsurface rock. Azurite showcases a characteristic deep blue to violet blue colour, traditionally called azure (hence the name), and forms either tabular or prismatic glittering crystals with a vitreous luster in a wide variety of crystal habits, from rossette-shaped crystalline aggregates to massive (shapeless, no distinctive external crystal shape), nodular, stalactitic or botryoidal (globular) forms. 

 

Azurite is one of the two common basic copper (II) carbonate variations, the other being malachite, with bright green hues. The copper (II) content in these two minerals is reponsible for their bright blue and green hues, and also for their high specific gravity of 3.7-3.9, exceptionally high for a non-metallic mineral. Being more unstable in open air conditions, azurite is often pseudomorphically replaced by malachite over time, one mineral replacing another in a substitution process where the appearance and dimensions remain constant. Both azurite and malachite are thus are often found together in the same geological settings and the same specimens (as we can see in the large specimen of Fig. 25), although azurite is markedly less abundant than malachite. Both variations are also associated with native copper, cuprite (a copper oxide) and various iron oxide minerals. 

Fig. 33 - Azurite infographic from the RBA collection (in Spanish)

  Also, here are a couple of videos showcasing the rich colour and glittering crystals of my large azurite specimen ✨ (also on TikTok here and here):

✨Some interesting historical and STEM trivia about azurite:   

• "Azure" comes from Old French asur/azur, from Medieval Latin azzurum/azolum, via the Persian lazhuward, “blue" and the Arabic lāzaward "heaven, sky". This is the same etymology that appears in the also blue mineral lapis lazuli. Azurite has been known since Ancient times, mentioned by Pliny the Elder's Natural History under the Greek name κυανός (kuanos) "deep blue" (root of 'cyan'), and the Latin caeruleus "dark blue" (root of 'cerulean'). During the 19th Century, azurite was also known as chessylite after the French locality of Chessy-les-Mines, where azurite was mined.

• Uses: Even though it is not an abundant mineral, the bright blue tones of azurite have attracted attention for thousands of years, and it has been used since Ancient times for various uses, especially as a pigment (see below) and as a gemstone, cut into beads, cabochons, carvings and various types of jewellery and ornaments (even though it's brittleness and low hardness, as well as its oxidation into malachite with time, limits its use an an ornamental stone). Cultures such as the Ancient Egyptians also used it as an ore of copper, although nowadays the presence of azurite is mainly used in prospecting only as a surface indicator of the presence of copper sulfide ores. Another modern use of azurite is its interest for mineralogy collectors, due to its intense azure colour. 

• Azurite as a pigment: As early as the Ancient Mesopotamian and Egyptian cultures, azurite was already being ground to use as a blue pigment, as well as fused with glass. While Romans don't appear to have used it significantly, it was also used in Ancient Greece. A common mineral in Europe, it was during the Middle Ages and the Renaissance that the use of azurite for art became commonplace, becoming the main blue pigment used by Medieval artists and vastly surpasing the use of lapis lazuli, which had to be imported from Afghanistan. Because azurite weathers into malachite with time and exposure to light and the atmosphere, older paintings using azurite can show deterioration of the blue tones, with greenish tints appearing due to malachite. And, while its use was commonplace for centuries, making pigment from azurite was also quite costly, as it was difficult to mine, transport and produce. In the 18th Century, its use started to be replaced by human-made synthetic blue pigments such as "Prussian blue" and "blue verditer", more uniform and permanent in use and less costly to produce. 

Fig. 34 - Medieval women painting women, using azurite among other pigments (note the man grinding azurite in the illumination on the right). Manuscript illuminations from Boccacio's De Claris Mulieribus.

Bonus, 17) Chalcanthite (pentahydrate copper(II) sulphate):

Fig. 35 - A crystallized synthetic specimen of pentahydrate copper(II) sulphate (left), and a chalcanthite specimen (naturally ocurring copper sulphate) (right), both from my existing collection.

Fig. 36 - A synthetic specimen of chalcanthite, showcasing beautiful prismatic crystals

Fig. 37 - A chalcanthite specimen with a tabular crystal habit

Fig. 38 - a chalcanthite specimen

Fig. 39 - A synthetic specimen of chalcanthite

Another blue copper mineral that I wanted to talk about in this post is chalcanthite (pentahydrate of copper sulphate). It does not feature in the RBA collection, but I have two lovely specimens that I got years ago in a memorabilia shop in Segovia (Castilla y León, Spain) (Figs.  35-39), so I'm including them in this post as well. One of them is a naturally ocurring chancanthite from Riotinto (Huelva, Spain) (Figs. 37-38), while the other one  (Figs. 36 and 39) is a synthetic specimen of (pentahydrate) copper sulphate. These are also among my fave specimens in my collection, because of their striking electric blue shades, and also because of the beautiful crystallization pattern of the synthesized specimen  (Figs. 36 and 39).

Fig. 40 - Chalcanthite infographic (Source)

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

 Copper(II) sulphate (CuSO₄) is an inorganic compound which forms hydrates with the chemical formula CuSO₄·nH₂O (where n can range from 1 to 7). The most common is the pentahydrate (n=5) of copper sulphate (CuSO₄·5H₂O), a bright blue water-soluble crystal, occurring in nature as the chalcanthite mineral, and also as rarer minerals such as chalcocyanite. It can also be produced industrially by treating copper metal or copper oxides with hot sulfuric acid. Other names for this pentahydrate include blue vitriol, vitriol of copper, bluestone and Roman vitriol. 

Chalcanthite is found in late-stage oxidation areas of copper deposits. Due to the rapid solubility of this mineral, it is typically in arid regions and dry caves, commonly forming both botryoidal (globular) and stalactitic growths on walls and ceilings. The most notable feature of this mineral is its striking electric blue colour, and it dissolves in water, turning the solution blue. 

 

Natural chalcanthite crystals, typically tabular (shaped like a book) or prismatic, are very rare in nature, and most well-formed crystals are actually grown synthetically (as seen in the specimen of Figs. 36 and 39), dissolving readily-made copper sulphate and letting the water evaporate, leaving a beautifully crystallized mass of chalcanthite as the result. Large synthetic specimens of crystallized chalcanthite are sometimes unethically sold as being natural.

  Here's a short video, with a rather yellowish background, but the electric blues, and the way that the light shines off the crystals of especially the synthetic specimen, still show:

 ✨Some interesting historical and STEM trivia about chalcanthite:   

•  The name "chalcanthite" means "copper flower", describing the curved and flowering formations of this mineral, originating from the Ancient Greek χάλκανθον (khálkanthon), from χαλκός (khalkós) "copper", and ἄνθος (ánthos) "flower, bloom". 

• Copper(II) sulphate is a poisonous substance which can induce dangerous copper poisoning when consumed (so don't taste-test any copper sulphate solutions at home :S!).
  

• Uses: Chalcanthite can be used as an ore of copper in arid regions where it is found in suficiently large quantities. Its rich blue hues and beautiful crystals (be they naturally ocurring or synthesized) also make this a mineral that is highly sought out by mineralogy collectors, with the specimens needing to be adequately stored in order to protect them from humidity and preserve their crystalline structure. however, due to their rapid sollubility (I store both of my specimens in a closed wooden box).   Copper(II) sulphate in general also has various uses, mainly in industry and art: Among others, it  has been used as a fungicide, insecticide and herbicide; as a mordant in vegetable dyeing (dissolved copper sulphate also dyes materials in blue tones and highlights the green tints of some dyes); as a colouring ingredient in glasses and potteries; and as an additive for both book-binding glues, and to make concrete more resistant to water.
  
   

 -Finally, here are some infographics from the collection (in Spanish) about red jasper, Iceland spar, obsidian and azurite (click on the pics or open in new tab for larger pics!):

 

 

That's it for today! On the next minerals post we'll talk about: desert rose, aragonite, emerald, and jadeite 😃💎

💎Former posts in this series💎:

Post 1: Various types of quartz (rose quartz, Tiger's Eye, amethyst, ametrine and blue agate), as well as gold, fluorite, and celestine. Also check out this same first post for a lengthy rant about what I think about the pseudoscientific branches having to do with rocks, minerals and gems, such as 'crystal healing' (spoiler alert, I'm not a fan).

Post 2: Fuchsite, rhodonite, quartz and agate geodes, pyrite and galena.