Cookeite
Cookeite is just a mineral that is silicate is an associate for the Chlorite Group of minerals that also includes Chamosite and Clinochlore amongst others. Cookeite was discovered in 1866 and named for Josiah B. Cooke, Jr. (1827-1894), United states chemist and mineralogist, Harvard University, Cambridge, Massachusetts, USA. Cookeite has cleavage that is ideal micaceoius fracture and is flexible but inelastic with waxy or greasy luster with pearly luster on basal cleavages. It can be found in colors of white, yellowish green, green, pink, colorless or brown when pure. A sky that is rare or bluish green to deep green variety of Cookeite can be found as micaceous, spherulitic balls on colorless Quartz crystals at the Stand-on-Your-Head # 1 mine (Alum Creek possibility), Bland, Saline County, Arkansas, USA. The picture above shows an inclusion of the single, pale ball that is green of in clear, colorless Quartz from Minas Gerais, Brazil.
Areas for Cookeite: good examples from: in the USA, at Hebron, Mt. Mica, near Paris, and Buckfield, Oxford County, Maine; in the Pala and Rincon districts, San Diego County, Ca; from the Jeffrey quarry, North Little Rock, Pulaski County, Arkansas. At Waitabit Creek, northwest of Donald, British Columbia, Canada. From Ogofau, Carmarthenshire, England. At Radkovice and Dobrá Voda, Czech Republic. Within the Varuträsk pegmatite, 15 km northwest of Skellefteå, Västerbotten, Sweden. From Lipovka, Ural Mountains, Russia. Within the Muiâne pegmatite, Alto Ligonha district, Mozambique. At Londonderry, Western Australia. At Itambé, Bahia and Conselheiro Pena, Doce Valley, Minas Gerais, Brazil. Many localities that are additional known.
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| Chemical Formula: | LiAl4(Si3Al)O10(OH)8 |
| Lithium Aluminum Silicate Hydroxide | |
| Molecular Weight: | 522.16 gm |
| Composition: | Lithium | 1.33 % | Li | 2.86 % | Li2O |
| Aluminum | 25.84 % | Al | 48.82 % | Al2O3 | |
| Silicon | 16.14 % | Si | 34.52 % | SiO2 | |
| Hydrogen | 1.54 % | H | 13.80 % | H2O | |
| Oxygen | 55.15 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Monoclinic – Prismatic |
| Crystal Habit: | Pseudohexagonal platy crystals; curved, radial scales, spherulites, barrel-shaped, fibrous. |
| Twinning: | Around [310], composition plane {001}; frequently shows six sector twins by polarized light microscopy |
| Cleavage: | Perfecct on {001} |
| Fracture: | Micaceous |
| Tenacity: | Flexible but inelastic |
| Moh’s Hardness: | 2.5 – 3.5 |
| Density: | 2.58 – 2.69 (g/cm3) |
| Luminescence: | May fluoresce creamy yellow under SW UV |
| Radioactivity: | Not Radioactive |
| Color: | White, yellowish green, pink, brown; colorless to pale green or pink in thin section. Colorless when pure. |
| Transparency: | Transparent to translucent |
| Luster: | Waxy, greasy; pearly or silky on basal cleavage |
| Refractive Index: | 1.572 – 1.600 Biaxial ( + ) |
| Birefringence: | 0.014 – 0.024 |
| Dispersion: | r < v |
| Pleochroism: | Visible; X = Y = pale green to pink; Z = colorless to pale yellow |
