Sphalerite is ZnS, Zinc sulphide, a major ore of zinc. The specimens location is unknown, but included in my collection as a "type specimen" The crystals are small, only two mm on average. They are well formed tetrahedral crystals which on first inspection appear black in colour, however, when viewed under high magnification the crystals are an intensely deep red in colour. There are also minor amounts of calcite, and quartz scattered around the specimen.
Microcline feldspar has the formula of KAlSi3O8, and is sometimes referred to as potassium feldspar or K-feldspar. It is dimorphous with orthoclase, and is a major constituent of granite, and common in felsic igneous rocks. The specimen is typical of others from Papachacra, Belen department, Catamarca province, Argentina. It is mainly composed of beige-pink crystals of microcline and is peppered with crystals of smoky quartz.
Wulfenite is a secondary mineral of lead and is a lead molybdate with the formula of PbMoO4 Wulfenite can be a vibrant colour of orange, but can also be very variable in colour, ranging from orange to yellow and brown. This specimen is coloured a dull orange, bordering on brown. The crystals are tabular with a rectangular shape and for the most part are intersecting each other. Unfortunately the origin of the specimen is not known, but is in my collection as a "type" specimen.
There are many badly formed prismatic crystals of quartz, SiO2 lining this cavity in sandstone. The crystals are colourless, but many appear to be dull orange in colour, due to a dusty coating of possibly an iron mineral. The specimen is from Tan y Foel quarry at Cefn Coch in Powys. The quarry is in the Penstrowed grits formation of Mid Silurian age.
This is a rather unusual specimen that has two major components, silica SiO2 and calcite CaCO3 It obviously started life as a silica geode, but about 30% of the centre has been invaded by a growth of massive calcite. For the main, the inner cavity is lined with miniscule quartz crystals, with a number of "stalks " composed of almost microscopic druzy quartz crystals. There are quite a number of very small doubly terminated quartz crystals, which would put them in the category of "Herkimer" diamonds. There are also quite a number of very small calcite rhombs. In the small inset picture a small rhombohedral calcite crystal is mounted on one of those Herkimer- type crystals. The specimen is from Dulcote hill in the Mendip Hills. from workings that closed in the mid 1970s.