Arsenopyrite

Arsenopyrite is a metallic mineral made of iron, arsenic and sulfur, coloured between silver-white and steel-grey. About 46 per cent of its weight is arsenic. It is the most abundant and widespread arsenic mineral in the Earth’s crust and one of the main ores of arsenic. It occurs in hot veins, often together with gold, and its name is a contraction of a phrase meaning “arsenical pyrites”.

Arsenic ore: Arsenopyrite is one of the main ores of arsenic. Arsenic is used today mainly in lead alloys (batteries, ammunition) and semiconductors (gallium arsenide); it has also been used in wood preservatives, weedkillers and insecticides. Industrial arsenic is mostly recovered as a by-product from the dust of copper, gold and lead smelters. A pointer in gold prospecting: Because it can occur with gold, it is treated as an indicator of gold-bearing veins. Collecting: Its lustrous, sharp crystals appear in mineral collections, but because it is poisonous it must be stored with care.

It has a hardness of 5.5–6 on the Mohs scale. It can scratch glass; a steel knife scratches it only with difficulty. Its specific gravity is 5.9–6.2 g/cm³.

Its best-known localities: Tavistock, Devon, England; Freiberg, Saxony, Germany; Panasqueira, Castelo Branco, Portugal; Boliden, Västerbotten, Sweden; Cobalt district, Ontario, Canada.

Known localities in Türkiye: Karabaşvengi, Divriği, Sivas, Türkiye.

Its colour lies between silver-white and steel-grey; it is not golden yellow like pyrite and chalcopyrite. The lustre is metallic and the streak is black. Its hardness is 5.5–6, clearly harder than copper sulfides such as bornite, covellite and chalcocite. It is very dense (specific gravity 5.9–6.2): it feels heavy for its size.

On the “street to diamond” value ladder it sits on step 4 of nine: Fine dimension stone and ore. Arsenopyrite is not valued as an ore in its own right: arsenic is poisonous, its uses are limited and it needs extra precautions in processing, so its worth mostly depends on the gold it contains or accompanies. In many arsenopyrite gold ores the gold is locked inside the mineral and cannot be recovered easily with cyanide, which raises the cost of processing. For collectors, sharp, lustrous, undamaged crystals and specimens from famous deposits such as Freiberg or Panasqueira are sought.

Arsenopyrite contains about 46 per cent arsenic by weight; it is poisonous if swallowed or if its dust is breathed in. Do not lick it, put it in your mouth or eat it; never put it in water to make “gem water” or an “elixir”. Do not heat it (poisonous arsenic fumes are released), do not break it to sniff it, and do not crush or sand it. On exposure to air it slowly turns into iron arsenates; do not touch specimens whose surface has started to decay with bare hands, and do not breathe their dust. According to the World Health Organization, long exposure to arsenic can cause skin, bladder and lung cancer. Wash your hands after handling. Keep specimens away from children and pets, in a closed container.