A monoclinic mineral, 2(Ni₃(AsO₄)₂.8H₂O) ; vivianite group with cobalt replacing nickel toward erythrite; occurs as light-green soft coatings of fine striated crystals, or 134 earthy; an oxidation product of nickel and cobalt arsenides, the green crusts being a distinctive guide to nickel ores. Formerly called nickel ocher. Compare: nickel bloom