The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Crystallography||Monoclinic. Crystals prismatic, tabular, equant; in clusters, radial groups. Also massive, bladed, fibrous; crusts, earthy masses.|
|Refractive Index||1.569 - 1.675|
|Colors||Colorless (fresh); darkens to shades of green and blue, then dark green, dark bluish green, dark purplish, bluish black.|
|Luster||Vitreous, pearly on cleavage; also dull, earthy.|
|Polish Luster||Vitreous, pearly on cleavage|
|Specific Gravity||2.64 - 2.68|
|Cleavage||Perfect 1 direction. Fracture fibrous. Thin pieces are flexible and sectile.|
|Stone Sizes||Faceted gems are rarely cut because the material is so soft and fragile. The cleavage is almost micaceous, making it very difficult to polish gems. The Bolivian material for example could cut stones up to 75-100 carats (indices are 1.585/1.603/1.639, S.G. 2.64).|
|Transparency||Transparent to Opaque|
|Absorption Spectrum||Not diagnostic|
|Identifying Characteristics||Color fade|
|Formula||Fe3(PO4)2 · 8H2O.|
|Pleochroism||Intense: blue/pale yellowish green/ pale yellowish green; or deep blue/pale bluish green/pale yellow green; or indigo/yellowish green/yellowish olive-green.|
Colorless, then dark blue after a time.
a= 1.569-1.516; β=1.602-1.656; γ=1.629-1.675.
Biaxial (+) ZV: 63-830.
A secondary mineral in ore veins: also occurs as an alteration product of primary phosphate minerals in granite pegmatites; forms as sedimentary concretions.
- Colorado; California; New Jersey; Delaware; Maryland; Florida.
- Canada; Australia; Japan; Germany; USSR; France; England.
- Lemhi County, Idaho: fine crystals.
- Bingham Canyon, Utah: crystals to 5 inches in length.
- Richmond, Virginia: good crystals.
- Black Hills, South Dakota: in pegmatites.
- Llallagua and Poopo, Bolivia: fine cuttable crystals to 6 inches long.
- N’gaoundere, Cameroon: massive crystals up to 4 feet long, dark in color, cuttable.
Vivianite is so fragile and soft that cut gems would be difficult to handle safely, let alone wear. The material darkens spontaneously, so the color of an attractive stone might disappear after a time, making it less enticing to spend the time cutting such material. The color of vivianite is very rich, and a few stones have been cut anyway.
Odontolite is a phosphate (actually fossil bone and teeth) that has been stained by vivianite and may resemble turquoise.
After J. G. Vivian, an English mineralogist who discovered the species.