annabergite

{{Infobox mineral | name = Annabergite | boxwidth = | boxbgcolor = | image = Annabergite-Siderite- Grece-1.jpg | imagesize = 260px | alt = | caption = Annabergite (green) from Lavrion, Greece | category = Arsenate minerals | formula = Ni3(AsO4)2·8H2O |IMAsymbol=Anb | molweight = | strunz = 8.CE.40 | dana = | system = Monoclinic | class = Prismatic (2/m) (same H-M symbol) | symmetry = C2/m | unit cell = a = 10.179(2), b = 13.309(3) c = 4.725(1) [Å]; β = 105(1)°; Z = 2 | color = Apple-green, pale green, pale rose or pale pink, white, gray; may be zoned | colour = | habit = Usually as fibrous veinlets, crystalline crusts, or earthy; rare as well formed crystals | twinning = | cleavage = Perfect on {010}, indistinct on {100} and {102} | fracture = | tenacity = Sectile | mohs = 1.5–2.5 | luster = Subadamantine, pearly on cleavages, may be dull or earthy | streak = Pale green to white | diaphaneity = Transparent to translucent | gravity = 3.07 | density = | polish = | opticalprop = Biaxial (−) | refractive = nα = 1.622 nβ = 1.658 nγ = 1.687 | birefringence = δ = 0.065 | pleochroism = | 2V = Measured: 84° | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = | impurities = | alteration = | other = | references = }}

Annabergite is an arsenate mineral consisting of a hydrous nickel arsenate. It is considered a member of the vivianite group and known for its ability to form crystals in a characteristic apple-green color.