Sulfides: Pyrite

Composition: FeS₂; nickel and cobalt may substitute for iron

Crystal system: Isometric; crystals commonly cubic, also pyritohedral or octahedral, also massive

7.10.1
pyrite crystals with quartz

Properties:

• Metallic lustre
• Brassy yellow color
• Dark streak (greenish to brownish black)
• Knife will not scratch (Mohs Hardness 6-6.5)
• High density
• Cleavage not obvious
• Conchoidal fracture
• Not ferromagnetic
• Does not reacts with hydrochloric acid (HCl)

Occurrence:

Pyrite is the most common sulfide mineral. It occurs as an accessory mineral in igneous and metamorphic rocks and with other sulfides in hydrothermal ore deposits, including vein, replacement and massive sulfide deposits.

7.10.2
pyrite crystals with quartz

Pyrite is rarely of economic value as a source of sulfur (not iron); however, the presence of significant amounts of pyrite may indicate that other economically important sulfides and precious metals occur in the immediate environment. Acid mine drainage as a result of the weathering of pyrite in mine waste and unmined ore or coal is a significant environmental problem.