Iron sulphide. The name of the mineral comes from the Greek root pyr, meaning "fire," because it is one of the stones that produces sparks if struck by iron.

Crystal system Cubic.
Appearance It occurs as cubic crystals with striated faces, or in the form of pentagonal dodecahedra, usually well-crystallized, either isolated or in small, often well formed groups. It is a characteristic, brassy yellow or pale gold color, opaque and with a metallic luster. It sometimes occurs as nodules or concretions, consisting of aggregates of minute crystals.

Physical properties It has a hardness of 6-6.5 and a density of about 5.0-5.2 g/cma. It is brittle and will crumble beneath a hammer blow, unlike gold, with which it has even been confused (the popular name is fool's gold). The powder is (again, unlike gold) black or grayish.

Genesis Very common and widely distributed, it is deposited both by magmatic segregation from basic rocks and as a result of intrusive processes in general, especially during hydrothermal phases. it also occurs in certain sedimentary environments.

Occurrence Large deposits are found the world over. but those of Spain, Italy, Norway, Sweden, Germany. Japan, and the United States are famous. Very well formed crystals or nodules are also found away from major deposits.

Pyrite
Pyrite was and still is employed as an ornamental material, on account of its luster, its elegant crystal form, the appearance of some roughly radial concretions or certain groups of crystals, and the fact that it can be cut and polished. it is often confused with the dimorph marcasite another, very similar mineral of the same color which is much less common and has orthorhombic symmetry. In fact the misnomer is now so widespread that it is nearly always referred to as marcaaite when used for ornamental purposes, even it the obvious cubic crystal form leaves no doubt as to its being pyrite. If anything, it is the concreted nodules of sedimentary origin that could occasionally be marcasite.

Appearance Isolated cubes with striated faces, pentagonal dodecahedra, or small groups of these two forms with their natural facets are normally used, aithough sometimes the nodules are used instead. These consist of minute crystals with a flattened, radial structure, a minutely granular surface and the characteristic. metallic yellow color. Small stones (2 to 3 millimeters in diameter} have sometimes been given a flattened circular, rose cut with only three polished facets on top. They are generally set in White metal, tor obvious reasons of contrast, and are sometimes merely glued, rather than set, onto their supports.They are often found on necklace clasps and old—fashioned, inexpensive brooches. '

Distinctive features In uncut stones, the shape of the crystal combined with the color, luster, and high density, or the form of the nodules. are unmistakable. Even when cut. its appearance is unique.

Occurrence It is very common and widely distributed throughout the world, even in the qualities suitable for ornamental purposes.

Value Extremely low.

Simutants and synthetics Because of its widespread occurrence, it is neither imitated nor produced synthetically.