| Celestine | |
|---|---|
 Clear grey-blue celestine crystals | |
| General | |
| Category | Sulfate minerals |
| Formula | SrSO4 sometimes contains minor calcium and/or barium |
| IMA symbol | Clt[1] |
| 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 |
| Ultravioletfluorescence | yellow, white blue (both short and long UV) |
| References | [2][3][4][5] |
Celestine (theIMA-accepted name)[6] orcelestite[1][7][a] is amineral consisting ofstrontium sulfate (SrSO4). The mineral is named for its occasional delicateblue color. Celestine and thecarbonate mineralstrontianite are the principal sources of theelementstrontium, commonly used infireworks and in variousmetal alloys.
Celestine derives its name from theLatin wordcaelestis meaning celestial[8] which in turn is derived from the Latin wordcaelum meaning sky, air, weather, atmosphere and heaven.[9]
Celestine occurs ascrystals, and also in compact massive and fibrous forms. It is mostly found insedimentary rocks, often associated with the mineralsgypsum,anhydrite, andhalite. On occasion in some localities, it may also be found withsulfur inclusions.
The mineral is found worldwide, usually in small quantities. Pale blue crystal specimens are found inMadagascar. White and orange variants also occurred atYate,Bristol, UK, where it was extracted for commercial purposes until April 1991.[10]
The skeletons of theprotozoanAcantharea are made of celestine, unlike those of otherradiolarians which are made ofsilica.
In carbonate marine sediments, burial dissolution is a recognized mechanism of celestine precipitation.[11] It is sometimes used as a gemstone.[12]
Celestine crystals are found in some geodes. The world's largest knowngeode, a celestine geode 35 feet (11 m) in diameter at its widest point, is located near the village ofPut-in-Bay, Ohio, onSouth Bass Island inLake Erie. The geode has been converted into a viewing cave,Crystal Cave, with the crystals which once composed the floor of the geode removed. The geode has celestine crystals as wide as 18 inches (46 cm) across, estimated to weigh up to 300 pounds (140 kg) each.
Celestine geodes are understood to form by replacement ofalabaster nodules consisting of thecalcium sulfates gypsum or anhydrite. Calcium sulfate is sparingly soluble, but strontium sulfate is mostly insoluble. Strontium-bearing solutions that come into contact with calcium sulfate nodules dissolve the calcium away, leaving a cavity. The strontium is immediately precipitated as celestine, with the crystals growing into the newly formed cavity.[13][14][15]
