Marcasite
North West Bohemia, Czechoslovakia
This specimen measures 8cm x 5.5cm
Marcasite FeS2
Sulfides; disulfide of iron
Color and Luster: Pale brass-yellow to almost white; tarnish deeper yellow to brown; metallic; streak dark greenish to brownish
Hardness: 6-6.5
Cleavage: Distinct, two directions
Fracture: Uneven, brittle
Crystals: Orthorhombic; dipyramidal; commonly tabular, rarely capillary; also stalactitic with radiating structure and botryoidal or reniform crusts; twin crystals showing coxcomb and spear shapes are common
Photo by Mary Sutherland
Descriptions taken from
The Audubon Society Field Guide to North American Rocks and Minerals