mineral

Arsenopyrite with Quartz

Arsenopyrite (FeAsS)

Hardness of 5.5-6 on the Mohs scale. Metallic luster with an opaque, silver-white to steel-grey color. It has a monoclinic crystal system and often forms columnar, bladed, or acicular crystals. It has a high specific gravity of 5.9-6.2 and distinct cleavage in two directions.

Identified December 29, 2025More mineral →

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Physical properties

Formation & geological history

Formed in high-temperature hydrothermal veins, pegmatites, and contact metamorphic deposits. It is often found in association with gold, silver, tin, and tungsten ores. It can be found in rocks from various geological ages, often from the Paleozoic to the Mesozoic.

Uses & applications

Primary ore of arsenic, which is used in the manufacture of pesticides, herbicides, and wood preservatives. It is also an important source of gold and silver in some deposits. High-quality specimens are valued by mineral collectors for their metallic luster and distinctive crystal forms.

Geological facts

When struck with a hammer or heated, arsenopyrite gives off a garlic-like odor, which is a characteristic sign of arsenic release. Historically, it was a common source of arsenic for medicine and poisons. Some of the finest specimens come from mines in China, Portugal, and Mexico.

Field identification & locations

Identify in the field by its metallic, silvery-grey appearance and the distinct garlic smell when crushed. It is heavy for its size and relatively hard. Common locations include high-temperature ore veins in Cornwall, England; the Panasqueira mine in Portugal; and various locations in China and Canada.