worldjewels.org

This mineral is a disulphide of iron, and in the cut form known as marcasite, it is widely used in medium priced jewelry. Actu­ally, marcasite is the rhombic modification of iron pyrites. In color, it is black with a yellowish tinge, but when polished, it has a bright, metallic luster which renders it suitable for use as small stones in a variety of settings. The luster is retained for some time since the hardness is 6 1/2, but the material is brittle and may be easily cracked.

The rough occurs in crystals of the cubic system and also as nodules in many sandstones, limestones, and shales. Specific gravity is about 5, which is high. The marcasite form of iron pyrites crystallizes in the rhombic system, and the material is widely distributed, both in crystal and in massive forms. Cumber­land provides much of the material which is sent to Germany for cutting. France also produces both the rough and the cut stone. The latter is used in quite small sizes, and it is usually fashioned as a flat rosette with just a few facets. When mounted in conjunc­tion with the cheaper colored stones, according to prevailing fashion, marcasite is very effective in rings, brooches, earrings, and bracelets. Formerly, it was also much used in buckles.

Although hard and heavy, this mineral has the disadvantage of being easily cracked by a knock. This causes the stone to fall from its setting, and marcasite set jewelry must therefore be treated with care. The stone is attacked and decomposed by nitric acid, but it is unaffected by hydrochloric acid. If struck with steel, it emits brilliant sparks; if heated, sulphur dioxide is given off, and it burns with a blue flame. The wide occurrence of iron pyrites has facilitated its use in jewelry from early times. Large polished pieces in the form of mirrors have been found in ancient graves in South America. Many pieces of jewelry of the last century were mounted with pieces of small cut steel, which somewhat resembles marcasite, but the latter material does not rust, as does steel, and it is more easily worked into small rosette shapes than the artificial alloy. The brass yellow specks seen in lapis lazuli are granules of iron pyrites, and not gold, as is often thought. Some pyrites do con­tain a little gold, and in some instances, it is present in sufficient quantity to be worth extracting.

Iron pyrites was once used instead of flint in the old wheel-lock fire arms, since it produces a spark when struck against steel.