Mineral Species: Boulangerite and Pyrite

Chemical Formula: Pb5Sb4S11

Chemical Name: Lead Antimony Sulfide

Mineral Class: Sulphosalt

Mineral Notes: Boulangerite is one of a few sulfide minerals that form hair-like fibrous crystals. The aggregates may be so thick as to entirely cover a matrix or single needles that are lodged between other minerals. Jamesonite and Millerite are two other sulfides that form similar crystals and can be mistaken for Boulangerite. However, Millerite is yellow and Jamesonite has brittle crystals. Boulangerite is a Sulfosalt, a type of Sulfide where Antimony acts like a metal and occupies a position where it is bonded to Sulphur. Boulangerite and Jamesonite are called feather ores. A variety of Boulangerite is called "plumosite" due to its feathery tufts and was once believed to be a different mineral.

Description: An almost solid mass of fused Pyrite crystals between which lie mats of horizontal gey-black Boulangerite needles. These are best seen under magnification but the form and habit are absolutely superb. This is an almost perfect example of this interesting mineral species.

Location: Naica, Mexico.