Polybasite - (Ag,Cu)₁₆(Sb,As)₂S₁₁

Habit: Iron-black, tabular, pseudohexagonal crystals, often showing triangular Striations or can be massive. Metallic Luster, opaque except in thin fragments, transparent.

Environment: In silver veins of low to medium temperature of formation

Etymology: From the Greek for many and base, in allusion to the many Metallic bases present. Can sometimes occur in sufficient quantities to be a significant ore mineral of silver.