Prosopite
Prosopite is a rare halide mineral that is commonly found as granular or powdery masses or as minute colorless crystals to about 6 mm. The chemical formula of Prosopite is CaAl2F6(OH)2 (Calcium Aluminum Flouride Hydroxide) and its molecular weight is 242.05 gm. Prosopite is usually a nondescript mineral of no gem significance except for the beautiful turquoise to sky blue material found at the Santa Rosa Mine, Noche Buena, Zacatecas, Mexico. This source has produced small quantities of massive material of turquoise to sky blue that can be made into beautiful cabochons (see picture above). This is the only location to produce such beautiful blue material large enough for gem use. Blue Prosopite from Zacatecas, Mexico may appear very similar to light colored Turquoise from various sources. Distinction from Turquoise is mainly based on the lower refractive index (1.50 vs. 1.62 for Turquoise). This blue Prosopite gets its color from approximately 1.4% Copper content.
Prosopite is found at the following localities: In Germany, from Altenberg, Saxony. At Horní Slavkov (Schlaggenwald), Czech Republic. From Perga, Volyn, Ukraine. In Russia, from Miass, Ilmen Mountains, Southern Ural Mountains; on the Yenisei Ridge, Siberia; and in the Zharchikhinsk molybdenum deposit, on the west side of Lake Baikal, eastern Siberia. In the Ivigtut cryolite deposit, southwestern Greenland. From Mt. Bischoff, Tasmania, Australia. In the USA, at St. Peters Dome, near Pikes Peak, El Paso County, and in the Goldie carbonatite, McClure Mountain-Iron Mountain, Fremont County, Colorado; in the Dugway district, Tooele County, Utah; at the Zapot pegmatite, 25 km northeast of Hawthorne, Fitting district, Mineral County, Nevada; from the Grand Reef mine, Aravaipa district, Graham County, and 16 km north of Bouse, La Paz County, Arizona; in the Morefield pegmatite mine, Amelia, Amelia County, Virginia. In Mexico, at the Santa Rosa mine, Mazapil, Zacatecas, Mexico. From Tsumeb, Namibia.
| Chemical Formula: | CaAl2F6(OH)2 |
| Calcium Aluminum Flouride Hydroxide | |
| Molecular Weight: | 242.05 gm |
| Composition: | Calcium | 16.56 % | Ca | 23.17 % | CaO |
| Aluminum | 22.29 % | Al | 42.12 % | Al2O3 | |
| Hydrogen | 0.83 % | H | 7.44 % | H2O | |
| Oxygen | 13.22 % | O | |||
| Fluorine | 47.09 % | F | 47.09 % | F | |
| — % | F | -19.83 % | -O = F2 | ||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Monoclinic – Prismatic |
| Crystal Habit: | Crystals, prismatic || [001], flattened on {010}, with {021}, {111}, and {221} also noted, to 6 mm; commonly granular or powdery. |
| Twinning: | None |
| Cleavage: | Perfect on {111} |
| Fracture: | Irregular/Uneven to Conchoidal |
| Tenacity: | Brittle |
| Moh’s Hardness: | 4.5 |
| Density: | 2.880 – 2.894 (g/cm3) |
| Luminescence: | May be fluorescent; sky blue to bluish white under SW UV and LW UV |
| Radioactivity: | Not Radioactive |
| Color: | Colorless, Grayish to White, rarely Turquoise-Blue; Colorless in transmitted light. |
| Transparency: | Transparent when fresh; becomes translucent on exposure. |
| Luster: | Vitreous, weak |
| Refractive Index: | 1.500 – 1.510 Biaxial ( + ) |
| Birefringence: | 0.009 |
| Dispersion: | None |
| Pleochroism: | None |
