Boulangerite

Boulangerite is one of a few sulfide minerals that form fine acicular crystals that appear as hair-like fibers. The fibrous aggregates may be so thick as to cover a specimen with hair-like fibers or it may be sparsely disseminated between other minerals and may be confused with actual hairs or dark lint. Jamesonite and millerite are two other sulfides that form similar acicular crystals and can be mistaken for Boulangerite. However, millerite is yellow and Jamesonite has brittle crystals. Boulangerite is a sulfosalt, a segment of sulfides where the antimony acts more like a metal than a non-metal and occupies a position where it is bonded to sulfurs. Boulangerite and Jamesonite have been called feather ores. A variety of Boulangerite is called "plumosite" due to its plumose (feathery) habit and was thought to be a different mineral.