Marcasite

Formula: FeS2

Colour: Pale brass-yellow, tin-white on fresh exposures.

Lustre: Metallic, Sub-Metallic

Hardness: 6 – 6½

Specific Gravity: 4.887

Crystal System: Orthorhombic

Member of: Marcasite Group

Name: Early use of the word marcasite seems to have been unspecific. The word is Arabic or Moorish and was applied to pyrite and similar metallic bronze colored minerals. In 1845, Wilhelm Karl von Haidinger defined marcasite as the mineral is known today.

The orthorhombic polymorph of isometric (cubic) pyrite. A common natural disulfide. Crystals common, metallic pale brass-yellow colored, tabular or pyramidal, often with curved faces and often deeply striated. It may also be stalactic, globular, or reniform with a radiating internal structure. Frequently found replacing organic matter, forming fossils, in sedimentary beds, particularly coal beds.
May be intergrown or replaced by pyrite.