Chalcocite
Cu 2 S has three homogeneous multi-image variants. An orthorhombic variant that is stable below 103 ° C; a hexagonal variant that is stable above this temperature to 420 ° C; an isoaxially crystalline variant that is stable above 420 ° C. High temperature equiaxed Hui copper ore with anti-fluorite structure; high-temperature hexagonal structure chalcocite, expressed as S hexagonal closest packing. The structure of the low-temperature orthorhombic chalcopyrite is quite complicated, and only the most widely distributed Cu 2 S low-temperature variants are described here.
[Chemical composition] often contains Ag, sometimes containing Fe, Co, Ni, As, Au, etc., some of which are mechanical mixtures.
[Crystal structure] orthorhombic system; 
a 0 = 1.192 nm, b 0 = 2.733 nm, c 0 = 1.344 nm; Z = 96.
[Formation] Single crystal is extremely rare. The crystal form is a pseudo-square short column or a thick plate. It is usually a dense, powdery (smoke-like) aggregate (Figure L-25).
Figure L-25 Powdered copper ore aggregate
[Physical properties] Fresh face gray and black weathered surfaces; dark gray streaks; metallic luster. opaque. No clerk. Hardness 2 to 3. The relative density is 5.5 to 5.8. Slightly malleable. A good conductor of electricity.
[genesis and occurrence] There are two causes of endogenous and exogenous. Endogenous people are found in late-stage hydrothermal copper deposits rich in Cu-poor S, often co-existing with porphyrite. Copper oxide found in the lower portion of the outer brilliance with some copper sulfide deposits, oxidation with copper sulphate solution and diafiltration down native sulfide (chalcopyrite, bornite, pyrite, etc.) metasomatism product. The chalcopyrite is very unstable in the surface environment and is easily decomposed into copper oxide and copper carbonate. Under incomplete oxidation, it can be converted into natural copper.
[Identification features] Dark lead gray, low hardness, weak ductility, small knife marks appear bright groove marks. Often with other copper
Minerals are symbiotic or associated.
[Main use] is the most abundant sulfide in copper, and is an important ore mineral of copper.
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