Celestine (mineral)
Celestine (the IMA-accepted name) or celestite is a mineral consisting of strontium sulfate (SrSO4). The mineral is named for its occasional delicate blue color. Celestine and the carbonate mineral strontianite are the principal sources of the element strontium, commonly used in fireworks and in various metal alloys.
| Celestine | |
|---|---|
Clear grey-blue celestine crystals | |
| General | |
| Category | Sulfate minerals |
| Formula (repeating unit) | SrSO4 sometimes contains minor calcium and/or barium |
| IMA symbol | Clt |
| Strunz classification | 7.AD.35 |
| Crystal system | Orthorhombic |
| Crystal class | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
| Space group | Pnma |
| Unit cell | a = 8.359 Å, b = 5.352 Å, c = 6.866 Å; Z = 4 |
| Identification | |
| Color | White, pink, pale green, pale brown, black, pale blue, reddish, greyish; colourless or lightly tinted in transmitted light |
| Crystal habit | Tabular to pyramidal crystals, also fibrous, lamellar, earthy, massive granular |
| Cleavage | Perfect on {001}, good on {210}, poor on {010} |
| Fracture | Uneven |
| Tenacity | Brittle |
| Mohs scale hardness | 3.0–3.5 |
| Luster | Vitreous, pearly on cleavages |
| Streak | white |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 3.95–3.97 |
| Optical properties | Biaxial (+) |
| Refractive index | nα = 1.619–1.622 nβ = 1.622–1.624 nγ = 1.630–1.632 |
| Birefringence | δ = 0.011 |
| Pleochroism | Weak |
| 2V angle | Measured: 50°–51° |
| Dispersion | Moderate r < v |
| Ultraviolet fluorescence | yellow, white blue (both short and long UV) |
| References | |
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