Obsidian "Apache tear"

Obsidian "Apache tear"

Obsidian is a volcanic glass classed as a mineraloid, and is composed of approximately 70 % Silica, SiO2, This Apache tear variety is formed as as the result of the differential cooling of siliceous, rhyolitic lava flows. The grey mineral surrounding the obsidian is perlite, an amorphous volcanic glass. The name Apache tear is attributed to an Apache legend. Apaches were fighting U.S. cavalry on a mountain overlooking Superior in Arizona. With no hope of winning they rode their horses off the mountain, and their families shed tears which turned to stone on hitting the ground. There are six towns named Superior in the U.S.,and this specimen comes from Superior, Colorado.

Baryte on calcite.

Baryte on calcite.

Baryte, BaSO4 Barium, sulphate. Specimens such as this one are very distinctive, and easily recognisable as coming from the Isle of Sheppey. The Isle is largely formed from the London clay. Within the clay are found septarian nodules coated with yellowy brown calcite resembling marzipan, upon which are perched radiating crystals of baryte. Even though there has been much research, the process of how they are formed is still a mystery.

Fluorite.

Fluorite.

Fluorite is calcium fluoride, CaF2  It may be called fluorspar, and is a halide mineral. In a pure form Fluorite is colourless and transparent, however it is an allochromatic mineral and is very variable in colour because of the inclusion of trace elements. This specimen is light purple in colour and is a slab of well formed and intergrown cubic crystals on a limestone matrix. The location is loosely given as Egremont  in Cumbria.

Astrophyllite

Astrophyllite

Astrophyllite is a highly complex mineral, a hydrous, potassium, iron, titanium, silicate. with a formula of (K,Na)3 (Fe++,Mn)7 Ti2 Si8 O24 (O,OH)7 It is usually found in the form of a bladed stellate aggregate, often in a radiating form. ( astron from the Greek for star, and pyllon, also from the Greek for leaf ). It is not a common mineral and is found in only a few locations, for instance this specimen came from the Kola peninsula in Russia.  

Baryte, Shelve

Baryte, Shelve

Baryte, BaSO4,  Barium sulphide,  is a common gangue mineral associated with lead ore deposits, and this applies to this specimen collected from the White grit mine, Shelve, in Shropshire. The specimen appears to be structured in layers, and is quite heavy at 9 Kg. I remember that I made an improvised rucksack to carry it about half a mile, by tying the sleeves of my jumper together. Baryte is also a useful mineral, with about two thirds of world production used as a weighting agent in oil drilling