ACANTHITE
Acanthite (a.k.a. argentite) is a scarce silver
sulfide mineral - Ag2S. On fresh surfaces, acanthite has a
metallic silvery-gray appearance. On less fresh surfaces, it's got a dull
metallic luster and a dark gray to black-colored tarnish. Acanthite lacks
cleavage, has a black streak, is fairly soft (H = 2 to 2.5), and is fairly
heavy for its size. Acanthite is the
most important silver ore mineral.
Acanthite (argentite) (9 mm across along the base) from the Imiter Mine, Imiter
Silver Deposit, Anti-Atlas Mountains, central Morocco. Ore mineralization
at Imiter has been dated to ~550 million years (near-latest Neoproterozoic).