Marcasite
Mineral FeS2
Also called White iron pyrites, Cockscomb pyrite, and Spear pyrites
Take care.
- Breaks down in damp air: Keep it dry and in steady humidity; some crumble or rot as they take on moisture.
About it
Paler than pyrite, often as cockscomb or spear-shaped crystals and radiating nodules in chalk and clay. Decays to white powder and acid in damp air. Known from the English Chalk, Missouri, and Czechia.
- Type
- Mineral
- Group
- Sulfide, marcasite group
- Formula
- FeS2
- Hardness (Mohs)
- 6–6.5
- Specific gravity
- 4.85–4.9
- Streak
- greyish black to brownish black
- Lustre
- metallic
- Crystal system
- Orthorhombic
- Colours
- pale brass yellow, tin white, tarnishing yellowish
- Transparency
- opaque
- Cleavage and fracture
- poor; uneven fracture, brittle
Typical values: real specimens vary. For more, see mindat.org.