Colemanite
Colemanite (Ca2B6O11·5H2O) or (CaB3O4(OH)3·H2O) is a borate mineral found in evaporite deposits of alkaline lacustrine environments. Colemanite is a secondary mineral that forms by alteration of borax and ulexite.
| Colemanite | |
|---|---|
| General | |
| Category | Inoborates |
| Formula (repeating unit) | Ca2B6O11·5H2O |
| IMA symbol | Cole |
| Strunz classification | 6.CB.10 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | P21/a |
| Unit cell | a = 8.712(2) Å, b = 11.247(3) Å, c = 6.091(1) Å; β = 110.12°; Z = 4 |
| Identification | |
| Color | Colorless, white, yellowish, grey |
| Crystal habit | Massive granular to coarsely crystalline, most commonly nodular. |
| Cleavage | [010] perfect, [001] distinct |
| Fracture | Brittle uneven to subconchoidal |
| Mohs scale hardness | 4.5 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 2.42 |
| Optical properties | Biaxial (+) |
| Refractive index | nα = 1.586 nβ = 1.592 nγ = 1.614 |
| Birefringence | δ = 0.028 |
| Fusibility | 1.5 |
| Diagnostic features | Exfoliates on heating, produces a green flame |
| Other characteristics | Bright pale yellow fluorescence, may phosphoresce pale green; pyroelectric and piezoelectric at very low temperature. |
| References | |
It was first described in 1884 for an occurrence near Furnace Creek in Death Valley and was named after William Tell Coleman (1824–1893), owner of the mine "Harmony Borax Works" where it was first found. At the time, Coleman had alternatively proposed the name "smithite" instead after his business associate Francis Marion Smith.
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