Gypsum, selenite var.

Gypsum, selenite var.

Gypsum, Calcium sulfate dihydrate,  CaSO4 . 2H2O  This specimen from Essone in France is referred to as selenite. However, selenite varieties of gypsum also includes desert rose, satin spar, and gypsum flower. The crystals of the specimen are clear and tabular with an angled termination. The crystals are relatively minute compared to the cave selenite crystals in the inset picture.

Pyrophyllite.

Pyrophyllite.

Pyrophyllite is a phyllosilicate mineral Al2Si4O10(OH)2 Aluminium silicate hydroxide. The crystalline folia habit is well represented in this specimen, which has the general location of California, USA. The specimen has a soapy feel, when handled.

Aragonite.

Aragonite.

Aragonite, Calcium carbonate, CaCO3  has the same chemical composition as calcite, and vaterite. These three minerals are polymorphs of calcium carbonate, each with a different crystal lattice, so each one with a different crystal habit. Aragonite crystals are often pseudohexagonal and prismatic, as are the twinned crystals in this specimen from Morocco. Aragonite is not a stable polymorph, and will eventually  alter to calcite.

Calcite.

Calcite.

Calcite, Calcium carbonate,  CaCO3 This specimen is one of many collected from Taffs Well quarry, Cardiff , South Wales. There are several varieties of crystal to be found at this quarry. In this specimen the crystals are stubby and prismatic, with a pale cream colouration. The crystals have quite obvious horizontal striations, and are growing from a base of massive calcite.

Labradorite.

Labradorite.

Labradorite, ((Ca,Na)(Al,Si)4O8   is a feldspar mineral and is an intermediate to calcic member of the plagioclase feldspar series. When polished it's iridescent properties are revealed in an effect known as labradorescence. For this reason, it is often used to make jewelery. This specimen displays the plagioclase content, which is usually 40" to 60%. and comes from Larvic in Norway.