Properties
| Category | Sulfide mineral |
|---|---|
| Formula | FeS2 |
| Crystal system | Orthorhombic |
| Color | Tin-white on fresh surface, pale bronze-yellow, darkening on exposure, iridescent tarnish |
| Crystal habit | Crystals typically tabular on {010}, curved faces common; stalactitic, reniform, massive; cockscomb and spearhead shapes due to twinning on {101}. |
| Cleavage | Cleavage: {101}, rather distinct; {110} in traces |
| Fracture | Irregular/Uneven |
| Tenacity | Brittle |
| Mohs scale hardness | 6–6.5 |
| Luster | Metallic |
| Streak | Dark-grey to black. |
| Diaphaneity | Opaque |
| Specific gravity | 4.875 calculated, 4.887 measured |
From the Wikipedia article
The mineral marcasite, sometimes called "white iron pyrite", is iron sulfide (FeS2) with orthorhombic crystal structure. It is physically and crystallographically distinct from pyrite, which is iron sulfide with cubic crystal structure. Both structures contain the disulfide S22− ion, having a short bonding distance between the sulfur atoms. The structures differ in how these di-anions are arranged around the Fe2+ cations. Marcasite is lighter and more brittle than pyrite. Specimens of marcasite often crumble and break up due to the unstable crystal structure.
Source
Source record: crystal-compendium/marcasite/minerals.json. Fetched from English Wikipedia by the operator 2 October 2026.
https://en.wikipedia.org/wiki/Marcasite — revision id 1369617789. Text and properties from Wikipedia, licensed CC BY-SA 4.0.