| Vivianite | |
|---|---|
Vivianite from the Foote Mine, North Carolina |
|
| General | |
| Category | Phosphate minerals |
| Chemical formula | Fe3(PO4)2•8(H2O) |
| Strunz classification | 08.CE.40 |
| Crystal symmetry | Monoclinic 2/m |
| Unit cell | a = 10.086 Å, b = 13.441 Å, c = 4.703 Å; β = 104.27°; Z = 2 |
| Identification | |
| Color | Colorless, very pale green, becoming dark blue, dark greenish blue, indigo-blue, then black with oxidation |
| Crystal habit | Flattened, elongated prismatic crystals, may be rounded or corroded; as stellate groups, incrustations, concretionary, earthy or powdery |
| Crystal system | Monoclinic prismatic |
| Twinning | Translation gliding |
| Cleavage | Perfect on {010} |
| Fracture | Fibrous |
| Tenacity | Flexible, sectile |
| Mohs scale hardness | 1.5-2 |
| Luster | Vitreous, pearly on the cleavage, dull when earthy |
| Streak | White, altering to dark blue, brown |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 2.68 |
| Optical properties | Biaxial (+) |
| Refractive index | nα = 1.579 - 1.616 nβ = 1.602 - 1.656 nγ = 1.629 - 1.675 |
| Birefringence | δ = 0.050 - 0.059 |
| Pleochroism | Visible; X = blue, deep blue, Indigo-blue; Y = pale yellowish green, pale bluish green, yellow-green; Z = pale yellowish green, olive-yellow |
| 2V angle | Measured: 63° to 83.5°, Calculated: 78° to 88° |
| Dispersion | r < v, weak |
| References | [1][2][3] |
Vivianite (Fe3(PO4)2•8(H2O)) is an iron phosphate mineral. It occurs as a secondary mineral found in a number of geological environments. It is usually found as deep blue to deep bluish green prismatic to flattened crystals.
It is formed by the alteration of ore deposits near the surface, or of primary phosphates in pegmatites. Vivianite crystals are often found inside fossil shells, such as those of bivalves and gastropods, or attached to fossil bone. Vivianite darkens upon exposure to oxygen.
Notable localities are Russia, Ukraine, Namibia, England, and Maryland, Colorado in the United States, and the town of Iwama, Japan.[4]
It was first described in 1817 and named after John Henry Vivian,[1][5] who first discovered crystals of the mineral in Cornwall, England. The type locality is Wheal Kind, in St Agnes, Cornwall.[2]