Annabergite, Nickel Arsenate,
Formula Ni3(AsO4)2.8H2O)

Crystal system: Monoclinic (crystals are rare)
Hardness: 1.5 to 2.5
Density: 3.1
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.

Annabergite, Lavrion, Greece.