annabergite

Annabergite is a hydrated nickel arsenate mineral with the chemical formula Ni3(AsO4)2 · 8H2O. It is a secondary mineral, meaning it forms as a result of the weathering and alteration of primary nickel and arsenic-bearing minerals. Annabergite typically crystallizes in the monoclinic system and is known for its distinctive pale green to emerald green color, which is due to the presence of nickel. It often forms as botryoidal, reniform, or earthy masses, and sometimes as delicate needle-like or prismatic crystals.

This mineral is relatively soft, with a Mohs hardness of 2.5 to 3, and has a specific gravity of around 3.0 to 3.1. Annabergite is often found in association with other nickel minerals such as garnierite and morenosite, as well as with arsenates of other metals like erythrite (cobalt bloom). It is typically found in arid or semi-arid environments where weathering processes are active.

The name "annabergite" comes from the town of Annaberg in Saxony, Germany, where it was first described. Notable occurrences include the Schneeberg district in Saxony, the Cobalt-Gowganda region in Ontario, Canada, and various locations in Australia and the United States. While not a primary ore of nickel due to its relatively low concentration and widespread distribution, annabergite can serve as an indicator mineral for the presence of nickel deposits. It is also collected by mineral enthusiasts for its attractive color and crystal habits.