mineral

Arsenopyrite in Quartz Matrix

Arsenopyrite (FeAsS)

Hardness: 5.5-6 (Mohs scale); Color: Silver-white to steel gray; Luster: Metallic; Crystal Structure: Monoclinic; Cleavage: Distinct; Specific Gravity: 5.9-6.2; Often produces a garlic-like odor when struck.

Hardness: 5
Color: Silver-white to steel gray
Luster: Metallic

Identified March 4, 2026More mineral →

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Physical properties

Formation & geological history

Formed in high-temperature hydrothermal veins, often associated with gold, tin, and tungsten deposits. Geological age varies by deposit, ranging from Precambrian to Cenozoic.

Uses & applications

Primary ore of arsenic; historically used for herbicides, glass manufacturing, and semi-conductors. It is often a key indicator for prospectors seeking gold deposits.

Geological facts

Arsenopyrite is the most common arsenic-bearing mineral. When heated or struck with a hammer, it releases toxic arsenic vapors and a distinct smell of garlic, which is a key diagnostic test.

Field identification & locations

Identify by its metallic silver sheen, high density, and garlic-like smell when crushed. Commonly found in Cornwall (UK), Germany, China, and Canada. Handle with gloves and wash hands after touching.