Boulangerite

Formula: Pb5Sb4S11 sulfosalt
Specific gravity: 6.0 to 6.3
Hardness: 2½ to 3
Streak: Brown to brown-grey
Colour: Lead-grey
Environments:

Hydrothermal environments

Boulangerite occurs in low to moderate temperature hydrothermal veins, associated with lead sulfosalts, galena, stibnite, sphalerite, pyrite, arsenopyrite, siderite and quartz.
Common impurities: Cu,Zn,Sn,Fe