Tsumoite
Tsumoite is a member of the Ingodite Group of minerals and contains only Bismuth and Tellurium with the chemical formula BiTe. It is a rare Bismuth Telluride mineral which is opaque, silver-white in color with a metallic luster. It is often found as tiny rounded hexagonal plates, from 1 to 5 mm, and as irregular aggregates often associated with Gold and Tellurobismuthite in a white Quartz matrix. The picture above shows tiny Tsumoite and Gold crystals in Quartz. If you hover your cursor over the picture it will show a magnified view of the silvery Tsumoite crystals and bright yellow Gold crystals and possible lead-gray Tellurobismuthite crystals on white Quartz. This rare gem comes from the Björkdal Mine, Sandfors, Västerbotten, Sweden.
Tsumoite is named after its discovery locality, the Tsumo Mine, Shimane Prefecture, Japan. The Tsumo Mine is located about 50 km northwest of Hiroshima City. The area comprises Paleozoic sedimentary rocks, their metamorphic equivalents, and acidic igneous rocks of late Cretaceous age. Although Tsumoite was discovered in 1972, it was not published until an article by Hidehiko Shimazaki and Tohru Ozawa in the 1978, volume 63, issue of American Mineralogist (1162–1165). The IMA also approved Tsumoite as a new mineral species in 1978.
Tsumoite distribution: from Japan, in the Tsumo mine, about 50 km northwest of Hiroshima City, Shimane Prefecture [Type Locality]. At the Dashuigou Tellurium deposit, Sichuan Province, China. In the Ban Phuc deposit, northwestern Vietnam. From the Kolar Gold Fields, Karnataka, India. In Russia, at the Tyrnyauz W–Mo deposit, left bank of the Baksan River Valley, northern Caucasus Mountains; in the Alekseevskoye mine, Sutam district, Stanovoi Range, southeast Sakha. From the Ransko massif, about 18 km east-northeast of Havličkův Brod, Czech Republic. At Úhorná, Slovakia. From the Bjorkdal gold mine, Vasterbotten, and at Tunaberg, Sweden. From Sylvanite, Hidalgo County, New Mexico, USA. In the Copper Cliff South mine, Sudbury, Ontario, Canada. A few additional poorly located localities are known.
| Chemical Formula: | BiTe |
| Bismuth Telluride | |
| Molecular Weight: | 336.58 gm |
| Composition: | Bismuth | 62.09 % | Bi | ||
| Tellurium | 37.91 % | Te | |||
| 100.00 % |
| Crystallography: | Trigonal – Hexagonal Scalenohedral |
| Crystal Habit: | As hexagonal plates, commonly rounded, to 5 mm, in irregular aggregates. |
| Twinning: | None |
| Cleavage: | Perfect on {0001} |
| Fracture: | n/a |
| Tenacity: | Brittle |
| Moh’s Hardness: | 2.5 – 3.0; Vickers: VHN100=51-90 kg/mm2 |
| Density: | 8.16 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioactive |
| Color: | Silver-white; in polished section, white with a creamy tint |
| Transparency: | Opaque |
| Luster: | Metallic |
| Refractive Index: | R1–R2: (400) 61.0–62.2, (420) 61.1–62.3, (440) 61.2–62.4, (460) 61.3–62.7, (480) 61.4–63.1, (500) 61.5–63.4, (520) 61.6–63.8, (540) 61.7–64.2, (560) 61.9–64.6, (580) 62.2–65.0, (600) 62.5–65.4, (620) 62.7–65.7, (640) 63.0–65.9, (660) 63.1–66.0, (680) 63.2–66.1, (700) 63.3–66.2 |
| Birefringence: | 0.000 (opaque) |
| Dispersion: | None |
| Pleochroism: | Very weak |
| Anisotropism: | Moderate |
