What is "guettardite"

n. (context mineral English) A monoclinic-prismatic grayish black mineral containing antimony, arsenic, lead, and sulfur.

Guettardite is a rare arsenic- antimony lead sulfosalt mineral with formula Pb(Sb,As)S. It forms gray black metallic prismatic to acicular crystals with monoclinic symmetry. It is a dimorph of the triclinic twinnite.