New Silicate Minerals Update 16 April 2021

16 April 2021

Our updates this week are based on chemical classifications and today it’s all about silicon bearing minerals. These naturally include the silicates and we have indulged ourselves by also including Quartz. Quartz, silicon dioxide, is the second commonest mineral found in the Earth’s crust, second only to Feldspar, so its inclusion in this update adds to the range of silicon containing species. The element silicon (Si) is the most prolific of the lighter elements which formed Earth, so as heavy elements sank towards the centre of the Earth during its formation, the lighter ones floated to the surface. Silicon was discovered by Jacob Berzelius in 1787 and the silicate group presently contains 1298 mineral species. In its native form, silicon is a hard crystalline solid with a silver metallic lustre and is classed as a metalloid or semi-metal, sitting in that zone of the periodic table between metals and non-metals. This is why silicon is a good semi-conductor. Today’s is a colourful and interesting selection, so let’s get cracking and see what’s on offer.

We will begin with silicon’s main oxide, Quartz, then move on to all the remaining silicates. It is well worth looking at all five specimens as they are all so different: a smoky Sceptre Quartz with fluid inclusions from Namibia; Amethyst from Mexico; a beautiful pair of quartz crystals encrusted with Pyrite and Siderite from Panasqueira mine in Portugal and from the Dodo mine in the Western-Siberian Region of Russia, a lovely lemon Citrine and mind-blowing Quartz Gwindel.

We tend to associate Gwindel Quartz with places like Switzerland and the French Alps, but this amazing museum quality specimen is Russian! Gwindel is the term for when Quartz crystals have grown sideways and parallel to their c-axis, and are characteristically twisted, forming an overall curved surface. On this specimen worm-like crystals of Clinochlore form a finely meshed net over the entire specimen making all surfaces appear sparkling dark green. However, when held against the light, the transparency of the specimen shines through, clearly defining the mesh of Clinochlore crystals. It is simply beautiful.

Beryl is a silicate, so we have included a magnificent thick prismatic Aquamarine from Pakistan; a pink Brazilian Morganite and a terrific Emerald with Calcite from Muzo in Colombia.

There are four great Topaz specimens; Topaz is an aluminium-fluorine silicate. From the Pamir Mountains in Tajikistan, a stunning pale sherry-tinged colourless crystal of water-clear Topaz emerges from a broad murky Quartz crystal of opaque orange brown. From Mina Veronica in Mexico, a fine thumbnail of colourless Topaz crystals which grade to red terminations. And from the famous Chamber Pegmatites at Volodarsk-Volynskii in the Ukraine, a choice crystal of pale smoky sky blue tinged reddish champaign Topaz nestles amongst blades of creamy off-white Albite Feldspar and a thick book of black grey Polylithionite Mica crystals.

Also, from these pegmatites we have a splendid good sized cabinet specimen of one single, ex-matrix clove brown Topaz crystal with frosted outer faces. When viewed along its c-axis through its cleaved base, the outer prism faces are sherry brown with an almost colourless interior of excellent transparency.

Tourmaline is a complex boron silicate which forms crystals compounded with many other elements. Have a look at the spectacular jet black Schorl measuring 20 cm long, formed from stacked sub-parallel Schorl clusters, each partly splayed outwards. This is a real beauty from Davib Ost Farm 61 in the Erongo Region of Namibia. Also look out for a Chrome Dravite from Tanzania and a wonderful Elbaite Tourmaline with Quartz from Coronel Murta in Brazil.

Splashes of extra colour are provided by an electric-blue Indian Cavansite, a bottle green Uvarovite Garnet from Finland and a gorgeous barley sugar orange Grossular Garnet from Tongbei in China.

The silicate minerals will always form the largest group of a species-systematic mineral collection and their variety of crystal habits, colours and textures will always impress. Enjoy looking through our 21 silicon-bearing minerals and you may discover something worth adding to your own collection.

Here is what you have to look forward to in next week's update:

Tuesday 20th & Friday 23rd April - England

                                         

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Author: JH
Categories: Updates

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