Annabergite, Nickel Arsenate,
Crystal system: Monoclinic (crystals are rare)
Hardness: 1.5 to 2.5
Colour: Apple green
Streak: Pale green to white
Annabergite is a rare secondary mineral formed by
oxidation of cobalt and nickel arsenides and
sulphides in hydrothermal deposits.
It is sometimes described as an apple green variant of Erythrite. Erythrite is a purple colour and is cobalt arsenate.
The mineral is named after Annaberg in Germany where it was originally found. The specimen in the picture came from Lavrion in Greece.