Volkonskoite
Volkonskoite is a rare chromium bearing silicate mineral that is relatively soft with a Mohs hardness of only 1-2 and a waxy to dull luster. Of the few Volkonskoite sources most produce uninteresting specimens. The one source that produces beautifully colored gem quality material is Mt. Efimyatskaya in the Ural Mountains of Russia. This massive material produces specimens large enough to be used for faceting small gems. The color ranges from olive green to bright grassy green. These colors combined with the waxy luster create beautiful and unusual gems.
Distribution: On Mt. Efimyatskaya and elsewhere in the Okhansk region, middle Kama River area, Permskaya Oblast’, Ural Mountains, Russia. In the Belgorod-Dnestrovskii (Akkerman) area, Ukraine. In Bulgaria, near Gotse Delchev (Nevrokop), Pirin Mountains. Fortullino, Rosignano Marittimo, Livorno Province, Tuscany, Italy. Kleggåsen Ruby Quarry, Froland, Aust-Agder, Norway.
| Chemical Formula: | Ca0.3(Cr3+,Mg,Fe3+)2(Si,Al)4O10(OH)2 •4H2O |
| Hydrated Calcium Chromium Magnesium Iron Silicate Hydroxide | |
| Molecular Weight: | 475.69 gm |
| Composition: | Calcium | 0.84 % | Ca | 1.18 % | CaO |
| Magnesium | 4.60 % | Mg | 7.63 % | MgO | |
| Aluminum | 2.84 % | Al | 5.36 % | Al2O3 | |
| Chromium | 13.12 % | Cr | 19.17 % | Cr2O3 | |
| Iron | 3.52 % | Fe | 5.04 % | Fe2O3 | |
| Silicon | 20.66 % | Si | 44.21 % | SiO2 | |
| Hydrogen | 1.95 % | H | 17.42 % | H2O | |
| Oxygen | 52.47 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Monoclinic – Prismatic |
| Crystal Habit: | Fine scaly to fibrous, massive |
| Twinning: | None |
| Cleavage: | Perfect on {001} |
| Fracture: | Conchoidal |
| Tenacity: | Brittle |
| Moh’s Hardness: | 1.0 – 2.0 |
| Density: | 2.11 – 2.36 (g/cm3) |
| Luminescence: | Not Fluorescent |
| Radioactivity: | Not Radioactive |
| Color: | Blue-Green, bright to dark Green, grass-Green emerald-Green; emerald-Green in transmitted light |
| Transparency: | Translucent, Opaque |
| Luster: | Waxy, Dull |
| Refractive Index: | 1.551 – 1.569 Biaxial ( – ) |
| Birefringence: | 0.018 |
| Dispersion: | Strong; r > v |
| Pleochroism: | None |
