Chalcopyrite & Pyrite on Dolomite (England) *AESTHETIC LITTLE SPECIMEN* for Sale

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Chalcopyrite & Pyrite on Dolomite (England) AESTHETIC LITTLE SPECIMEN For Sale

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Chalcopyrite & Pyrite on Dolomite (England) AESTHETIC LITTLE SPECIMEN:
$50.49

Small, well crystallised and isolated chalcopyrite crystals with cubic crystals of pyrite attached are spread over grey white dolomite crystals. From Greystone Quarry, Lezant, Cornwall, England, U.K., it measures 56x33x8 mm and weighs 17.47 g. A beautiful specimen, the largest crystal is approximately 3 mm.

Please note: this particular item is not large and is classed as a miniature-sized specimen (4.5-7 cm).

Greystone Quarry is a modern operation worked for road stone which is located 3 miles (5 km) south east of the town of Launceston and 7.5 miles (12 km) west of the edge of Dartmoor National Park. The quarry is situated on the strike of a lode system worked by several small 19th century lead mines (Greystone silver lead mine, Wheal Sophia, North Tamar) and cuts the eastern end of the vein system worked by the latter mine. Mineral extraction has occurred at Greystone Quarry since Victorian times, with the quarry first appearing on the 1st Edition 6” Ordnance Survey map of 1882. It has been operating since this time exploiting the high quality dolerite, an igneous rock which is geographically scarce in Cornwall, and which is known locally as “blue elvan”. This stone is a high specification aggregate suitable for use in specialist surfacing materials. The quarry walls at the locality are designated as the Greystone Quarry SSSI (Site of Special Scientific Interest) for its geological characteristics.

Chalcopyrite (a sulphide) is a copper iron sulphide mineral that crystallises in the tetragonal system. Commonly massive and sometimes botryoidal, it has a brassy to golden yellow colour and on exposure to air, chalcopyrite oxidises to a variety of oxides, hydroxides and sulphates. Associated copper minerals include the sulphides bornite, chalcocite, covellite, digenite; carbonates such as azurite and malachite, and rarely oxides such as cuprite. Rarely found in association with native copper, chalcopyrite is the most important copper ore. Mohs hardness 3.5.

Pyrite (a sulphide), or iron pyrite, is a very common mineral found in a wide variety of geological formations from sedimentary deposits to hydrothermal veins and as a constituent of metamorphic rocks. An iron sulphide, it’s considered the most common of the sulphide minerals. Pyrite can form in extremely well-crystallised examples of cubes, pyritohedrons, and octahedrons. Combinations of these forms also occur. An icosahedron formed from a combination of an octahedron and pyritohedron is also known. Pyrite crystals frequently form penetration twinning (crystal inter-growths), especially in the cubic form. Cubes are sometimes elongated in rectangular form. Also occurs massive, radiating, grainy, flaky, drusy, mammillary, encrusting, nodular, tuberose, fibrous, in concretions, and as groups of small crystals. Pyrite crystals are frequently striated, exhibiting tiny parallel line growths or grooves on the crystal faces. The metallic lustre and pale brass-yellow hues of pyrite has in many cases led to people mistaking it for gold, hence the common nickname 'fool's gold'. However, pyrite is quite easy to distinguish from gold: pyrite is much lighter, but harder than gold and cannot be scratched with a fingernail or pocket knife. Pyrite will slowly oxidise in a moist environment and release sulphuric acid that is formed during the process. However, whilst pyrite formed as sedimentary concretions has a tendency to decompose quickly, well-crystallised specimens are generally relatively stable. Mohs hardness 6-6.5.

Dolomite (a carbonate) is an anhydrous carbonate mineral composed of calcium magnesium carbonate. The colour can be white, grey to pink with a crystal habit of tabular crystals, often with curved faces, also columnar, stalactitic, granular and massive. A solid solution exists between dolomite, the iron-dominant ankerite and the manganese-dominant kutnohorite. Small amounts of iron in the structure give the crystals a yellow to brown tint. Manganese substitutes in the structure also up to about 3% manganese oxide. A high manganese content gives the crystals a rosy pink colour. Lead, zinc, and cobalt substitute in the structure for magnesium as well. In addition to being an industrial mineral with a number of uses, dolomite is highly valued by collectors and museums when it forms large, transparent crystals. Furthermore, the term dolomite is also used for a sedimentary carbonate rock composed mostly of the mineral dolomite, but an alternative name sometimes used for the dolomitic rock type is dolostone. Mohs hardness 3.5-4.