Uvarovite (Garnet)
Uvarovite is a rare member of the Garnet Group of minerals that includes Almandine, Andradite, Grossular, Pyrope, Spessartine and Uvarovite. Uvarovite has a beautiful emerald-green color and is the only consistenly green Garnet variety. The green color is due to the presence of chromium in its chemistry. The name has frequently been misused in the past to refer to other green and/or chromium-bearing garnets. Many so-called ‘Uvarovites’ are actually chromian Grossular, chromian Pyrope, green Andradite (the so-called Iranian ‘uvarovite’) or even the rare Knorringite (magnesium chromium garnet). Uvarovite crystals are rarely large enough for faceting and usually available only as “drusy” type cabochons.
Although Uvarovite is an uncommon Garnet, there are numerous localities. From the Saranovskii mine, Biserskoye, in the Gorozavod district, and other localities around Yekaterinburg (Sverdlovsk), Ural Mountains, Russia. Exceptional crystals from Outokumpu, Finland. From Pico do Posets, near Vénasque, Pyrenees, Spain. In Canada, at South Ham, Wolfe County, Quebec. In the USA, from Wood’s Chrome mine, Lancaster County, Pennsylvania; at Riddle, Grant County, Oregon; in the Red Ledge mine, near Washington, Nevada County, around Newcastle, Placer County, near New Idria, San Benito County, and elsewhere in California. On Taiwan, Formosa. From Ergani Maden and in the Kop Krom [chrome] mine, Kop Mountains, near Askale, Turkey.
| Category: | Nesosilicate |
| Chemical Formula: | Ca3Cr2(SiO4)3 |
| Calcium Chromium Silicate | |
| Molecular Weight: | 500.48 gm |
| Composition: | Calcium | 24.02 % | Ca | 33.61 % | CaO |
| Chromium | 20.78 % | Cr | 27.17 % | CrO | |
| Silicon | 16.84 % | Si | 36.02 % | SiO2 | |
| Oxygen | 38.36 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Isometric – Hexoctahedral |
| Crystal Habit: | Commonly as euhedral crystals, dodecahedra or trapezohedra, or in combination with other cubic forms, to 4.5 cm. Fine or coarse granular, compact, or massive. |
| Twinning: | None |
| Cleavage: | None |
| Fracture: | Irregular/Uneven to Conchoidal |
| Tenacity: | Brittle |
| Moh’s Hardness: | 6.5 – 7.0 |
| Density: | 3.77 – 3.81 (g/cm3) |
| Luminescence: | Fluorescent; red under SW UV and LW UV |
| Radioactivity: | Not Radioactive |
| Color: | Emerald-green to dark green; in thin section, green; may be sectored. |
| Transparency: | Transparent to Translucent |
| Luster: | Vitreous |
| Refractive Index: | 1.865 Isotropic |
| Birefringence: | 0.000 (Isotropic minerals have no birefringence) |
| Dispersion: | n/a |
| Pleochroism: | None |
| Anisotrophism: | May be weakly anisotropic due to strain or symmetry reduction (triclinic and orthorhombic varieties are known). |
