THE MINERAL BOULANGERITE

Chemistry: Pb5Sb4S11, Lead Antimony Sulfide
Class: Sulfides and Sulfosalts
Uses: Mineral specimens and as minor ore of lead.
Specimens

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 dessiminated 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.

PHYSICAL CHARACTERISTICS:

Color is blue lead gray to gray.
Luster is either metallic or silky.
Transparency: Crystals are opaque.
Crystal System: Monoclinic; 2/m
Crystal Habits include dense or sparse felted masses of acicular crystals. Also in fibrous and compact plumose (feathery) masses.
Cleavage is good in one direction parallel to the length.
Fracture is uneven.
Hardness is 2.5
Specific Gravity is 5.8 - 6.2 (heavier than average for metallic minerals)
Streak is gray to brown.
Associated Minerals include pyrite, sphalerite, galena, siderite, quartz and arsenopyrite.
Other Characteristics: Crystals are flexible.
Notable Occurrences include Trepca, in the former Yugoslavia; Pribram, in the former Czechoslovakia; Sala, Sweden; Hunan, China; Harz, Germany; Baja California, Mexico and at several locations in Idaho, Montana, Colorado, Washington and Nevada, USA.
Best Field Indicators are crystal habit, flexibility, associations, color and luster.