Pyrite

Physical Properties
Chemical formula FeS2
Class Sulfide
Crystal system Cubic
Habit Cubes
Pyritohedra
OctahedraStriated faces, combinations of forms,
and penetration twinning are common.
Color Brass yellow
Hardness 6 to 6.5
Specific gravity 5.1
Cleavage Poor {100}
Fracture Subconchoidal
Luster Metallic
Transparency Opaque
Streak Greenish black to greenish grey
after Perkins, 362

Pyrite in Hand Sample

Pyrite

Pyrite in greenschist

Pyrite in phyllite

Pyrite and coal

Pyrite with fibrous “tails” or “beards”

Pyrite in Archean-aged (!) conglomerate

Pyritized plant tissue (how cool is that‽) in Rockwell Formation diamictite

Pyrite in Thin Section

Like every other metallic mineral, pyrite is just opaque and black in thin section. However, unlike most other metallic minerals, it can often be identified as pyrite by its cubic shape.

Pyrite, PPL
Pyrite, XPL

Further Reading

Pyrite at webmineral.com

Pyrite at mindat.org