Annabergite, also known as nickel bloom and historically known as nickel ochre, is the nickel analogue to erythrite (cobalt bloom), with the chemical formula Ni3(AsO4)2 · 8H2O. Where cobalt bloom is a distinctive crimson/purple, annabergite is apple-green in colour. Like erythrite it has a hardness of 1.5-2.5, with the hardness differing on different cleavage faces. It occurs in series with erythrite, and when the ratio of Co:Ni is about 1:1, it is light pink, becoming white/grey to pale green to apple-green as the ratio of nickel to cobalt occurs.
Crystals are rare, but are generally flattened prismatic to acicular when formed; annabergite more commonly occurs as a green coating on nickel minerals. See also erythrite.
Sources:
Mindat
Wikipedia
Image 1: Annabergite crystals in a 1.9cm vug from Lavrion, Greece. irocks.com Image 2: Annabergite with cuprian smithsonite from Km-3 mine, Attica Prefecture, Greece. irocks.com