Beryl. Olary, Australia.

Beryl. Olary, Australia.

Beryl is a beryllium aluminium cyclosilicate with a formula of Be3Al2Si6O18  The best known varieties of beryl are emerald, aquamarine, and morganite ( pink beryl ) It occurs in many colours, yellow, black, green, pink, and colourless.  Unfortunately, this specimen does not have any visible whole crystals, although there are some still completely buried in the feldspar matrix. The visible broken crystals do have some interest, in that the hexagonal end terminations are black as are the outer surfaces,  while the exposed interiors are pink. which would not have been obvious, but for the damage. The specimen was collected by our club co-founder, Jim Nicholls, from the Triple Chance mine, in Olary, Australia.  

Actinolite with sphalerite.

Actinolite with sphalerite.

Actinolite is an amphibole silicate mineral with the formula Ca2(Mg4.5-2.5Fe2+0.5-2.5)Si8O22(OH)2   As the formula states, Mg and Fe are variables.  Mg and Fe ions are easily replaced in the crystal structure, with actinolite as an intermediate member in a series between magnesium rich tremolite, and iron rich ferro-actinolite. Fibrous actinolite is classed as an asbestos mineral. This specimen from South Wales, Australia is composed of actinolite and sphalerite with actinolite as the main component. The fibrous nature of actinolite can be seen in the inset, which is an enlargement of part of the main face, which has been cut and semi-polished. The sphalerite is "rubbly" in nature with no good crystals apparent.

Rhodochrosite. Broken Hill,Australia.

Rhodochrosite. Broken Hill,Australia.

Rhodochrosite,  MnCO3 is a manganese carbonate mineral, sometimes called mangano calcite. The substitution of calcite for manganese in the mineral leads to a pink coloration. Crystals of rhodochrosite are scalenahedral or rhombohedral, and are usually a deep pink colour. This specimen, from Broken Hill in Australia. is massive, with no crystals present.  

Bornite.

Bornite.

Bornite often has an iridescent surface, and for this reason is popularly known as "Peacock ore" It is a sulphide mineral, composed of copper and iron with the formula  Cu5FeS4   It is an important copper ore, widely occurring in porphyry copper deposits. There can be a wide variance in the amounts of copper and iron, and also a wide variance in coloration. This particular specimen, collected from Broken Hill in South Australia, is probably below average in brilliant coloration, but nevertheless is an interesting specimen.

Malachite, Brazil.

Malachite, Brazil.

Malachite is a copper carbonate mineral with the formula Cu2CO3(OH)2  Classed as a secondary mineral of copper, it occurs in the weathering zone, in proximity to major ore bodies. In it's purest form it contains 57% of pure copper, but this is not generally exploited because it is not plentiful enough, and because there is poor metallurgical recovery. It is quite a dense mineral with an s.g. of 3.6 to 4. and a hardness of 3.5 to 4. This polished slab appears to be a broken portion of a nugget, and is only known to have come from Brazil.