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.

Gypsum, altered.

Gypsum, altered.

Gypsum (CaSO4.2H2O)  calcium sulfate dihydrate is an evaporite mineral which can ocurr in many different colours, and crystal habits. The most common colour is  white or off white, and the most common crystal habit is in the form of selenite. This specimen collected from Barry harbour in South Wales in 2010. was lying on the beach, hence the light covering of algae. It has come from bands in the red marls in the cliff face. The original nodule has been altered by water passing through the rocks, which has left this crenulated specimen with nearly all the exposed surfaces coated with an alteration product of small scalenahedral crystals of calcite.

Rutile, Australia.

Rutile, Australia.

Rutile is titanium oxide, TiO2 It is a common accessory mineral in high-temperature and high-pressure metamorphic rocks and in igneous rocks. There is a wide colour variation, with the golden variety most sought after for decorative purposes.  The crystal form is usually slender and acicular. The crystals in this specimen are not very well defined, are short and stubby, and almost black. It was collected from Mount Crawford, South Australia.

Molybdenite.

Molybdenite.

Molebdynite is molybdenum disulfide, MoS2  It was at one time thought to be lead, and has a similar appearance. The small metallic crystals in this specimen are scattered throughout the quartz. It's origin is unknown.