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Occurs in Pinal County.

Chemical Formula: Ag2S

Specific Gravity: 7.2

Luster: Metallic

Hardness: 2-2.5

Acanthite is a silver sulfide mineral that is an important ore of silver. It has a dark gray to black color and is commonly found in silver-rich ore deposits.

Next Pinal County mineral: Actinolite

It is one of the primary minerals in the process of silver ore formation and is considered an important source of silver extraction.

Chemical Composition and Properties:

Formation and Occurrence:

Acanthite is formed as a primary mineral in silver ore deposits that have undergone certain geological processes:

  1. Hydrothermal Deposition: Acanthite is commonly associated with hydrothermal mineralization, which occurs when hot mineral-rich fluids are circulated through cracks and fractures in rocks. As these fluids cool and react with surrounding rocks, they deposit minerals like acanthite.
  2. Epithermal Veins: Acanthite is often found in epithermal vein systems, which are mineralized veins that form at relatively shallow depths within the Earth’s crust.

Relation to Silver Extraction:

Acanthite is not typically a direct source of commercial silver extraction due to its relatively low silver content and the challenges associated with its processing. Instead, acanthite often serves as an intermediary mineral in the transformation of primary silver minerals (like argentite) into secondary silver minerals (like native silver) during the supergene enrichment process. This enrichment process involves the weathering and alteration of primary ore minerals near the Earth’s surface.

Other Silver Minerals:

MinDat Acanthite