Pyrope (Garnet)
Pyrope is a member of the Garnet Group of minerals that includes Almandine, Andradite, Grossular, Pyrope, Spessartine and Uvarovite. The Chemical formula of Pyrope is Mg3Al2(SiO4)3 (Magnesium Aluminum Silicate) and its molecular weight is 403.13 gm.
Pyrope is the only variety of Garnet that is always a shade of red. Pyrope is also the only variety of Garnet whose common source is igneous rather than metamorphic rocks. Pyrope is difficult to distinguish from Almandine but is usually clearer and contains fewer internal flaws. Pyrope has a specific gravity of 3.582 (g/cm3) and the refractive index of 1.714 Isotropic. Pyrope and Almandine form a mineral series in which iron in Almandine substitutes for the magnesium in Pyrope. In fact, pure Pyrope is unknown in nature and always contains some Almandine and Spessartine components. Rhodolite is the result of the mixture of Pyrope and Almandine of about two to one (Pyrope to Almandine). Malaya is a mixture of Pyrope and Spessartine. Umbalite from the Umba Valley, Tanzania is also a mixture of Pyrope and Spessartine. Pyrope gems are usually fairly small and larger gems sold as Pyrope are most likely Almandines with a Pyrope component.
Some Pyropes show an interesting color change. Material from one location in Norway is wine red in incandescent light and violet in daylight. Some Pyrope from the Umba Valley in East Africa are Pyrope-Spessartines that are greenish blue in daylight and magenta in tungsten light.
Distribution: Widespread. The following localities have all produced substantial amounts of gem material. Around Merunice (Meronitz), Czech Republic. Immense crystals in the Dora-Maira massif, Parigi, near Martiniana Po, Piedmont, Italy. In Germany, from Zöblitz and Greifendorf, Saxony. From South Africa, especially at the diamond mines around Kimberley, Cape Province. Along the Umba River and in the Pare Mountains, Tanzania. In the USA, at Masons’ Mountain, near Cowee Creek, Macon County, North Carolina, and from Buell Park, near Fort Defiance, Apache County, Arizona. In Australia, 20 km from Bingara, New South Wales, and at Proston, Anakie, and Ruby Vale, Queensland. From San Martin and Quines, San Luis, Argentina. At Gravata, Pernambuco, Brazil.
| Category: | Nesosilicate |
| Chemical Formula: | Mg3Al2(SiO4)3 |
| Magnesium Aluminum Silicate | |
| Molecular Weight: | 403.13 gm |
| Composition: | Magnesium | 18.09 % | Mg | 29.99 % | MgO |
| Aluminum | 13.39 % | Al | 25.29 % | Al2O3 | |
| Silicon | 20.90 % | Si | 44.71 % | SiO2 | |
| Oxygen | 47.63 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Isometric – Hexoctahedral |
| Crystal Habit: | Subhedral to euhedral crystals, showing the dodecahedron or trapezohedral forms, to 20 cm; also granular, massive. |
| Twinning: | None |
| Cleavage: | None |
| Fracture: | Conchoidal |
| Tenacity: | Brittle |
| Moh’s Hardness: | 7.0 – 7.5 |
| Density: | 3.582 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioactive |
| Color: | Purple-red, pinkish red, red-orange, deep red to almost black; colorless to pink in thin section. |
| Transparency: | Transparent to Translucent |
| Luster: | Vitreous |
| Refractive Index: | 1.714 Isotropic |
| Birefringence: | 0.000 (Isotropic) |
| Dispersion: | 0.022 |
| Pleochroism: | None |
