Tetrahedrite
Tetrahedrite is a copper antimony sulfosalt mineral that is named for its common crystal form, the tetrahedron.It is one of the most common of the sulfosalts and its tpypical tetrahedron crystals can be quite attractive and interesting as mineral specimens. Tetrahedrite often contains a certain percentage of silver as an impurity and is mined as a minor ore. Some iron, zinc and/or silver is always present in Tetrahedrite, up to approximately 15%, as impurities. Tetrahedrite forms a solid solution series with the rather rare mineral Tennantite (Copper Arsenic Sulfide). The two share the same crystal structure but they differ in the percentage of arsenic versus antimony. Antimony rich specimens are Tetrahedrite while arsenic rich specimens are Tennantite. Tetrahedrite is flint-gray to iron-black and is included in my Black Gems page. Although fairly common as a mineral specimen, it is rarely available as a faceted gem although gems are very attractive with their metallic luster.
AThere are many locations for Tetrahedrite worldwide but I am only listing a few localities which have produced well-crystallized material. In Germany, from Freiberg, Saxony, and in the Harz Mountains, at Clausthal and Horhausen. From near Brixlegg, Tirol, Austria. At Botés, near Zlatna, and Cavnic (Kapnikbánya), Romania. In France, at Irazein, Ariège, France, a few exceptionally large crystals, and from Sainte-Marie-aux-Mines, Haut-Rhin. In Cornwall, England, at the Herodsfoot mine. In Algeria, from near Tenés and Mouzaía. In Bolivia, at the San José mine, Oruro. In Peru, from Casapalca, Junin, in the Huallanca and Quiruvilca districts, and at many other places. From the Noche Buena mine, Mazapil, and at the El Cobre mine, Concepción del Oro, Zacatecas, Mexico. In the USA, in the Daly-Judge and other mines, Park City district, Summit County, Utah. From the Nanisivik mine, Baffin Island, Nunavut, Canada.
| Chemical Formula: | Cu9Fe2+3Sb4S13 |
| Copper Iron Antimony Sulfide | |
| Molecular Weight: | 1643.31 gm |
| Composition: | Iron | 10.20 % | Fe | ||
| Copper | 34.80 % | Cu | |||
| Antimony | 29.64 % | Sb | |||
| Sulphur | 25.37 % | O | |||
| 100.00 % |
| Crystallography: | Isometric – Hextetrahedral |
| Crystal Habit: | Crystals are tetrahedral, to 15 cm; common as groups of parallel crystals; massive, coarse or fine and granular to compact. |
| Twinning: | On {111} around [111] as twin axis; contact and penetration twins, commonly repeated. |
| Cleavage: | None |
| Fracture: | Sub-Conchoidal |
| Tenacity: | Somewhat Brittle |
| Moh’s Hardness: | 3.0 – 4.5 |
| Density: | 4.97 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioactive |
| Color: | Flint-Gray to iron-Black to dull Black, cherry-Red in transmitted light; in polished section, Gray inclining to olive-Brown. |
| Transparency: | Opaque, except in very thin fragments. |
| Luster: | Metallic |
| Refractive Index: | 2.72 Isotropic |
| Birefringence: | 0.00 (Isotropic) |
| Dispersion: | None |
| Pleochroism: | None |
| Other: | Color in reflected light: Gray to olive Brown |
