Pyrite
The
mineral pyrite or
iron pyrite is
iron disulfide, FeS
2. It has isometric crystals that usually appear as cubes or pyritohedrons. It has a slightly uneven and conchoidal fracture, a
hardness of 6-6.5, and a
specific gravity of 4.95-5.10. Its metallic lustre and pale to normal
brass-yellow color have earned pyrite the name
fool's gold, but ironically enough small quantities of actual
gold can sometimes be found in pyrite. In fact, some auriferous pyrite is a very valuable
ore of gold, and others are excellent ores of
arsenic,
nickel,
cobalt and
copper. Pyrite is used in jewellery, such as necklaces, bracelets and rings, and is often referred to as marcasite in the gem trade. Although the two are similar, marcasite cannot be used in jewellery as it has a tendency to crumble and turn into powder.
A mass of interwoven pyrite crystals, 11 cm (4.0 in) long
Being found worldwide, Pyrite is the commonest of the sulfide minerals. It is usually found associated with other sulfides, or with oxides, in quartz veins, in sedimentary rock and metamorphic rock, in coal beds, and as the replacement mineral in fossils. Pyrites, interestingly, can show negative resistance, acting as radio detectors and have been used in oscillator circuits.
Pyrite is used in the production of sulphur dioxide for the paper industry and in the manufacture of sulphuric acid, though not as much as it used to be. The name pyrite is from the Greek word meaning fire, likely due to the sparks that result when pyrite is struck against steel. This capacity made it popular for use in early firearms such as the wheellock.
Varieties of Pyrite
- Arsenopyrite (FeAsS) is known as a major ore of arsenic. Unlike the cubical crystals of regular pyrite, A typical arsenopyrite crystal contains a diamond shaped dome atop a prismatic crystal. The crystals have sharp acute angles that are a marked contrast from other sulfides that generally have only obtuse angles. In the crystals, twinning is common, often bending the crystal and sometimes forming crosses, x's or stars. Crystals are also typically striated.
Arsenopyrite was previously thought to be orthorhombic, but recent analysis proves it as monoclinic.
See also