THE MINERAL BERTHIERITE

Chemistry: FeSb2S4 , Iron Antimony Sulfide.
Class: Sulfides
Uses: A minor ore of antimony and as mineral specimens.
Specimens

Berthierite is easily confused with the closely related mineral stibnite. The chemistry of berthierite differs from stibnite by having an additional sulfur and one iron ion. Characteristic wise, berthierite differs from stibnite in being found more frequently in acicular to fibrous clusters, having a brown streak and non flexible crystals.

PHYSICAL CHARACTERISTICS:

Color is brownish gray to dark brown.
Luster is metallic.
Transparency crystals are opaque.
Crystal System is orthorhombic; 2/m 2/m 2/m
Crystal Habits include acicular, fibrous or radiating crystals.
Cleavage is perfect in the lengthwise direction.
Fracture is uneven.
Hardness is 2.5 - 3
Specific Gravity is approximately 4.6+ (average for metallic minerals)
Streak is a dark brown.
Other Characteristics: Crystals are not flexible.
Associated Minerals include quartz, stibnite and other sulfides.
Notable Occurrences include France; Rumania; Colorado, USA; England and Germany.
Best Field Indicators are crystal habit, streak, softness and inflexibility of crystals.