Steacyite
Steacyite is a complex silicate mineral containing Thorium (Th). The Thorium causes Steacyite to be stongly radioactive and emitting alpha (α) and beta (ß) particles, but not gamma (γ) radiation. Steacyite was discovered in 1981 at the Poudrette Quarry, Mount Saint-Hilaire, Québec, Canada and named in 1982 by Guy Perrault and Jan T. Szymaňski in honor of Harold Robert Steacy (June 7, 1923 – April 7, 2012), mineralogist, former Curator of the National Mineral Collection, Geological Survey of Canada, for his contributions to Canadian mineralogy.
Steacyite is found as radiating crystals, twinned micro to elongated prismatic crystals, and massive material in colors of light to dark brown, beige, green and yellow. It is found as dark-brown twinned micro (sub-milimeter) crystals at the Poudrette Quarry in Canada but as relatively large (to 2 cm), yellow to light brown elongated prismatic crystals in purple Charoite at the Murunskii Massif in Russia.
Steacyite is only found in a few locations worldwide. At the Type Locality (TL) Poudrette Quarry, Mont Saint-Hilaire, Québec, Canada. On Rouma Isle, Los Islands, Guinea. In the Dara-i-Pioz massif, Alai Range, Tien Shan, Tajikistan. At the Murunskii Massif, Chara and Tokko Rivers Confluence, Aldan Shield, Sakha Republic (Saha Republic; Yakutia), Eastern-Siberian Region, Russia.
| Chemical Formula: | K1-x(Na;Ca)2ThSi8O20 (x = 0.2 to 0.4) |
| Potassium Sodium Calcium Thorium Manganese Silicate | |
| Molecular Weight: | 825.70 gm |
| Composition: | Potassium | 2.84 % | K | 3.42 % | K2O |
| Sodium | 1.95 % | Na | 2.63 % | Na2O | |
| Calcium | 3.40 % | Ca | 4.75 % | CaO | |
| Thorium | 25.29 % | Th | 28.78 % | ThO2 | |
| Manganese | 1.33 % | Mn | 1.72 % | MnO | |
| Silicon | 27.21 % | Si | 58.21 % | SiO2 | |
| Oxygen | 37.98 % | O | |||
| 100.00 % | 99.52 % | = TOTAL OXIDE |
| Crystallography: | Tetragonal – Ditetragonal Dipyramidal |
| Crystal Habit: | As crystals elongated || [001], terminated by {100} and {001}, to 2 mm; radiating, crystalline, massive. |
| Twinning: | Cruciform, by 90° rotation about [010]. |
| Cleavage: | None |
| Fracture: | Irregular/Uneven |
| Tenacity: | Brittle |
| Moh’s Hardness: | 5.0 |
| Density: | 2.95 (g/cm3) |
| Luminescence: | Radioactive; emitting alpha (α) and beta (ß) particles, but not gamma (γ) radiation. |
| Radioactivity: | Strong; GRapi = 506,988.54 (PPB) (Gamma Ray American Petroleum Institute Units) |
| Color: | Dark brown, beige, green, yellow. |
| Transparency: | Translucent, Opaque; Translucent to Transparent in thin section |
| Luster: | Vitreous, Greasy, Dull |
| Refractive Index: | 1.572 – 1.573 Uniiaxial ( – ) |
| Birefringence: | 0.0010 |
| Dispersion: | n/a |
| Pleochroism: | None |
