Marcasite has a long history of use as a decorative and jewelry material. However, this brassy colored, metallic stone is quite brittle and seldom seen in modern jewelry.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Crystallography||Orthorhombic. Crystals abundant, tabular, pyramidal, often with curved faces; also massive; granular; radial; globular; cockscomb-shaped aggregates.|
|Colors||Pale brassy yellow, green-yellow, brownish, to whitish.|
|Fracture||Fracture uneven. Brittle.|
|Cleavage||Distinct 1 direction.|
|Phenomena||May be iridescent.|
|Etymology||From the Arabic marqashītā for pyrite.|
|Occurrence||Marcasite forms at low temperatures, especially in sedimentary environments such as clays, shale, coal beds, and in low temperature veins.|
Despite marcasite’s relatively low hardness and distinct cleavage, many cultures have worked this material into objects of beauty. The Ancient Greeks made jewelry from marcasite. The Incas of South America polished large slabs of it as decorative objects. Gem cutters in the Victorian Era faceted this material into stones with flat backs. This popular style was known as the flattened-rose cut. Jewelry makers set them in white metal settings, such as rhodium-plated silver.
Nevertheless, much of the material found in these antique jewelry pieces is actually pyrite, a dimorph or polymorph of marcasite. These minerals share the same chemistry but have different crystal habits. (Pyrites have greater stability than marcasites for jewelry wear). For a time, they even shared the same name. Miners called common crystallized pyrite gemstones marcasites until the 19th century.
Marcasites leave a greenish black streak. However, never conduct a destructive streak test on a finished stone.
You may find steel imitations of this material. However, steel may be magnetic while marcasite is not.
This mineral is abundant and found throughout the world. Notable sources of gem material include:
- United States: Illinois; Kansas; Missouri; Oklahoma; Wisconsin.
- United Kingdom, England: in chalk deposits along the coast and at Folkestone.
- Austria; Bolivia; Czech Republic; France; Germany; Myanmar; Slovakia.
Massive material exists. Gem cutters can fashion cabochons of any desired size.
Since marcasite can react to moisture and release sulfuric acid, store specimens in low humidity, below 60%, and separate from other pieces. Avoid inhaling dust when cutting this material and wash your hands after handling.
Marcasites are quite brittle. A sharp blow can easily crack a stone and loosen it in its setting. Because of its fragility and reaction to moisture, jewelry use is not recommended.