Acanthite

Acanthite is a mineral that can be lead gray, gray, or coal in color and is made from crystals. Its name comes from the Greek word, akanta, meaning "arrow", or the Latin word argentum, meaning "silver". It is made of silver(I) sulfide.

It is found in Freiberg, Schneeberg, and Annaberg, Germany. Acanthite is not radioactive.