Vivianite
Chemical Formula	Fe3(PO4)2?8(H2O)
Species	Phosphates
Crystal System	Monoclinic
Mohs Scale	1-2
Specific Gravity	2.68
Color	Colorless, very pale green, becoming dark blue, dark greenish blue, indigo-blue, then black with oxidation
Streak	White, altering to dark blue, brown
Luster	Vitreous, Pearly, Dull
Refractive Index	n = 1.579 - 1.616 n = 1.602 - 1.656 n = 1.629 - 1.675
Diaphaneity	Transparent, Translucent
Cleavage	PerfectPerfect on , in traces on and .
Fracture	Fibrous
Crystal Habit：Flattened, elongated prismatic crystals, may be rounded or corroded; as stellate groups, incrustations, concretionary, earthy or powdery
Geological Setting：A secondary mineral found in a number of geologic environments: The oxidation zone of metal ore deposits, particularly associated with gossan; in granite pegmatites containing phosphate minerals; and in clays and glauconitic sediments, and in recent alluvial deposits replacing organic material, peat, lignite, bog iron ores and forest soils.