Temporarily listed in the mineral collection, Bauxite is actually a rock that is the main ore of aluminium.It is composed of the aluminium minerals, gibbsite, bohemite, and diapsore, with two iron oxides, haematite and goethite. It is also a source of gallium. The pisoliths in the specimen have a pleasing visual effect. From Garrone in France, I obtained the specimen to illustrate minerals and their source to a class of school children.
Smoky quartz SiO2. silicon dioxide, is quartz which has attained a darkening in colour as a result of free silicon formed from the quartz by natural irradiation. The amount of irradiation determines a range of colour from almost complete transparency to a very dark variety called morion. The mild colouration, as in this specimen is referred to as smoky quartz. Unfortunately, the origin of the specimen is not known.
These specimens of gypsum, CaSO4 . 2H2O were collected on the same day. Both had eroded from the cliff face on Penarth beach, in South Wales. The rocks exposed on Penarth beach are Trassic Keuper marls, the upper parts of which Have nodules of gypsum which were deposited from evaporation in a playa environment. Both specimens are the same size. One is massive gypsum with a hint of pink, and one seems to be a collection of fragments deposited on more structured layers. These are specimens which should probably be included in my rock collection, which may be put online at some time.
Lepidolite, Na(AlSi3O8). Simplified formula, is a member of the mica family. This specimen is composed of radiating , prismatic, dark lavender crystals of Lepidolite, terminating in a strange mushroom top or cap. Also on the specimen are very fine crystals of albite. The beauty of this specimen is very hard to convey with a photograph, and can only be truly appreciated with close examination by eye. The location is Minas Gerais, Brazil.
Jasper, SiO2, Silicon dioxide. is an aggregate of chalcedony and microgranular quartz, and may be coloured by inclusions of other minerals, usually iron, This specimen has attracted the variety name of leopardskin jasper. Its orbicular pattern is created by diffusion from centres, and the reddish colour is probably the result of iron inclusions. The small cavity is lined with very small crystals of quartz. The location of the specimen is loosely given as Spain.