mineralogue-blog

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Apologies for my recent inactivity. After my exams in a couple weeks from now I will work on making some posts and rebuilding the queue.

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Calcurmolite, Umohoite, β-Uranophane, Baryte

Mas d’Alary (Mas d’Alary MCO), Lodève, Hérault, Languedoc-Roussillon, France

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Kyanite and Metamorphic Facies

Kyanite (which I posted about a couple days ago) has another attribute I did not touch upon: it is used as an index mineral to provide geologists with clues to the environment a rock formed in. In the example of kyanite, its presence indicates that the surrounding rock was exposed to high pressures (over 4 kilobars) but fairly low temperatures, because those are the conditions it forms under and is stable under. Its polymorphs, andalusite and sillimanite, form under lower pressure or higher temperatures, respectively, and are index minerals for those conditions. These environments, indicated by these and other minerals, are known as metamorphic facies.

 Above: a diagram showing the conditions that the polymorphs of Al2SiO5 form under. Source.

By no means are the Al2SiO5 polymorphs the only series of minerals indicating formation conditions. Obviously, the usefulness of kyanite and its polymorphs depends on the chemical composition of the surrounding rocks. For other rock chemistries and other temperature and pressure ranges, there are different series of index minerals. This image on Wikimedia Commons and this Wikipedia page sums up the different facies and the environments they represent.

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Tourmaline; Himalaya Mine, Gem Hill, California

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Kyanite, a (commonly) blue silicate with the formula Al2SiO5, is a metamorphic mineral with a number of distinguishing properties. Firstly, it is usually blue, although it may also be white or grey, and much more rarely orange, yellow, or pink. Its elongated, bladed crystals and perfect cleavage (*prepares for boob jokes*) also aid in identification. Other crystal habits seen are columnar and tabular habits. An interesting characteristic is its varying hardness (between 5 .5 and 7), depending on its crystallographic direction. Another name for the mineral is disthene, although I’ve never actually heard it by any other name than kyanite, which originates from the Greek word kyanos, meaning “blue”. The French spelling cyanite was also used in the 19th and 20th centuries. Regardless of spelling or name, the mineral finds use in ceramics.

Sources:

Wikipedia | Mindat

Image: Kyanite by Parent Gery. Retrieved from the Commons.

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A specimen of orpiment, more reddish than yellow. Rob Lavinsky/irocks.com via the Commons. From Quiruvilca Mine, Peru.

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Sugilite is a rarish purple cyclosilicate mineral with the chemical formula KNa2(Fe,Mn,Al)2Li3Si12O30. It is in fact more commonly light brownish yellow in colour and fairly unattractive. It is named after the Japanese petrologist Ken-ichi Sugi (pronounced with a hard g), although English-speakers frequently mispronounce the name of the mineral, particularly after it became well-known after large quantities of more attractive purple specimens were discovered in South Africa.

It has a Mohs hardness of 6-6.5. It occurs in intrusive syenite rock in its type locality in Japan, in Quebec, Canada, but in its locality at the Wessels Mine in the Northern Cape Province of South Africa it occurs in a metamorphed manganese deposit. Both accompanying images are from the Wessels Mine locality. 

Sources:

Wikipedia | Mindat | Webmineral

Images by Rob Lavinsky via Wikimedia Commons. Links here and here.

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Gold

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Antlerite is a green copper sulphate mineral, with the chemical formula Cu3(SO4)(OH)4. Its colour ranges in shade from light green to emerald green to black, and is translucent with a pale green streak. It has a hardness of 3-3.5. Antlerite occurs in weathered zones of carbonate-poor copper deposits in arid areas. It was originally thought to be fairly rare, but was discovered to be the main ore at the Chuquicamata mine in Chile and Antler mine in Arizona, USA, the latter of which lends the mineral its name. Antlerite is soluble in dilute sulphuric acid; however it can be distinguished from similarly coloured malachite because it does not dissolve in hydrochloric acid (malachite does). It may also be confused with brochantite, with which it is closely related. However, antlerite is less common.

Sources:

Wikipedia | Mindat 

Image: Antlerite from Ingadanais Mines, Castelo Branco, Portugal, by Leon Hupperichs, via Wikimedia Commons. Picture width: 3mm.

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Cuprite from Tsumeb, Namibia.

Description from irocks.com:

A stunning specimen of Christamas-colors, with brilliant red cuprite of unusual quality for Tsumeb perched on green-colored calcite matrix. This was , to me, the premier cuprite specimen in the collection and it really leaps out, as it is incredibly sparkly in person and the many facets reflect light every which way.

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I know this was originally posted a while ago but I occasionally look through the tags of minerals I post about to make sure I’m not using the same images everyone else has, and this is really nice.

I’d like to add this image of the linarite crystals from the source here: 

I’m not entirely sure what the other minerals on this specimen are (the source only says “matrix”, but the blues and greens make for a very nice piece (and sorry bijoux-et-mineraux for dredging up an old post lol)

Linarite - Greece

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Selenite (gypsum) with inclusions of copper. From Mission Mine, Arizona, USA; credit to R. Lavinsky, image via the Commons.

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Linarite is an uncommon blue sulphate mineral with the chemical formula PbCu(SO­4) (OH)2. It is named after its type locality at Linares, Spain. It is typically translucent, possessing a deep azure blue colour similar to that of azurite. However, it is softer than azurite, with a hardness of only 2.5, and does not react with dilute hydrochloric acid as azurite does. It occurs in the oxidation zone of lead mineral deposits and forms through the oxidation of galena, chalcopyrite, and other copper sulphides. Crystals are tabular or prismatic, but are generally very small, often observed as encrustations of minute crystals on matrix. It has been observed to alter to antlerite and to cerussite with malachite.

Sources:

Wikipedia | mindat | webmineral 

Image 1: Linarite in a vug in quartz matrix from Wanlockhead, Scotland, UK. Credit: Rob Lavinsky via the Commons. Image 2: Gemmy, lustrous linarite crystals in a 2 cm vug from Caldbeck Fells, Cumbria, England, UK. Credit: R. Lavinsky via the Commons.

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AZURITE (Copper Carbonate) crystal from the Oumjrane Mine, Alnif, Morocco, Africa. This crystal photo taken at 20X with microscope.

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Cuprite (Cu2O) is a dark red oxide of copper (I). Crystals are often adamantine or submetallic in lustre, and streak is a shiny metallic brownish-red. Twins may be frequently observed, and crystals generally occur in the octahedral or cubic habit, with the exception of a fibrous variety is known as chalcotrichite. It is known colloquially as ruby copper for its deep red colour, which may at times near black. Its density is higher than average, with a specific gravity of 6.14. Its colour and brilliance might make it attractive as jewellery; however it is quite soft (with a hardness of 3.5 to 4), and crystals are usually too small to be faceted. The exception is cuprite from a deposit in Onganja, Namibia, which has produced a number of gem quality crystals later faceted. Only its softness prevents faceted cuprite from being one of the most valuable gemstones.

Sources:

Wikipedia

Mindat

All images are of the same specimen from irocks.com, which is a cluster of very nice Tsumeb cuprite crystals. 

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Nearly 300 followers! Thanks guys :D I started this blog only a couple months ago (around march iirc) and I wasn't really expecting a large amount of interest, but it's cool that there's so many other people with an interest in minerals and stuff, and I've come across a lot more tumblr geologists since I started this blog which is also pretty cool. I've never actually introduced myself or anything on this blog but I'm a teenaged guy with an interest in rocks & minerals (no shit). I've been collecting for as long as I can remember although my current collection is quite small. I like science and geology in particular and I'm planning on studying geophysics starting in September. In case anyone was interested in who's behind the blog lol

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Malachite psuedomorphed after copper from Tsumeb, Namibia. On the back of the specimen (second image) you can see wulfenite crystals on the specimen. From irocks.com