Vanadinite. Unknown origin.

Vanadinite. Unknown origin.

Vanadinite  Pb5(VO4)3Cl is a mineral which forms in the oxidation zones of lead deposits, and is commonly referred to as a secondary mineral of lead. It is in a series of minerals which include mimetite and pyromorphite. The crystals in this specimen are orange and hexagonal. but sadly the origin of this specimen is unknown.

Manganese ore.

Manganese ore.

Manganese ore can be quite complex in composition, however the known location and origin of these specimens is helpful. The specimens were collected from Hozatel mine, Port Elizabeth, South Africa. Ore from this mine is described as Hozatel super grade, which has a manganese content of approximately 38% together with finely intergrown braunite and manganese carbonate. The pinkish areas in the specimens are the carbonate, and one specimen has an obvious iron content. Manganese ore was mined here till the 1980s when zones of ferruginization made it become economically unviable. The specimens were collected by a club member at about this time.  

Carborundum

Carborundum

I offer no apology for including carborundum in my collection. I saw the specimen on a market stall amidst the bric a brac priced at £10, and I could not resist buying it. Carborundum is of course a manufactured mineral made from silicon and carbon. and is also known as silicon carbide. SiC.   The method for producing carborundum was patented in 1893 by Edward Goodrich Acherson, and since then it has been one of  the most important minerals in many production processes.  The life of Acherson is fascinating, and I recommend that the reader should take a close look at his activities. The irridescence is the result of a silicon coating on the mineral surface.

Malachite with Chrysocolla

Malachite with Chrysocolla

Malachite is a copper carbonate hydroxide with a formula of  Cu2CO3(OH)2. Chrysocolla is a  hydrated copper phyllosilicate mineral, and mineraloid. The formula is highly complex, and so it is omitted. This specimen of unknown origin is composed of a bed of very dark green microcystalline crystals of malachite, overlain with an encrustation of mineraloid chrysocolla in very small botriodal form.

Ferroan dolomite

Ferroan dolomite

Ferroan dolomite is a way of describing dolomite which has an iron content, which imparts a rusty brown colour. There is a running discussion on whether a particular specimen is either Ferroan dolomite, or Ankerite. A true analysis can only be conducted in a laboratory. I am inclined to believe that this specimen is Ferroan dolomite, both from appearance, and because it is recorded as being present at the location by the National Museum of Wales. I collected the specimen from Henfwlch mine, Nant y Moch reservoir, in central Wales. It is composed entirely of Ferroan dolomite,  Ca(Mg,Fe)(CO3)2   with inclusions of  fractured wall rock, and would be described as an example of hydraulic brecciation.