Celestine
Celestine, also spelled celestite, is strontium sulfate, SrSO4, and the primary ore of strontium, crystallizing in the orthorhombic system. It is best known for growing in delicate pale blue, tabular crystals, a color that gave the mineral its name from the Latin caelestis, meaning heavenly. Celestine often forms alongside gypsum and calcite in sedimentary evaporite settings, distinguishing it from most other sulfate minerals of hydrothermal origin.
Celestine properties at a glance
| Type | Minerals |
|---|---|
| Chemical formula | SrSO4 |
| Mohs hardness | 3–3.5 |
| Crystal system | Orthorhombic |
| Luster | Vitreous, pearly on cleavage |
| Streak | White |
| Cleavage | Perfect on {001}, good on {210} |
| Fracture | Uneven |
| Specific gravity | 3.95–3.97 |
| Transparency | Transparent to translucent |
| Common colors | Colorless, Pale blue, White, Gray, Light green, Orange (rare) |
| Rarity | common |
Geology & background
Celestine typically precipitates within sedimentary basins from strontium-enriched groundwater circulating through limestone and evaporite sequences, often lining cavities, geodes, and nodules formed as fluids passed through porous rock over long spans of geologic time. Some of the finest specimens in the world, including large geodes filled with sky-blue crystals several inches long, come from Madagascar's Sakoany region, while significant industrial deposits occur in Ohio's Put-in-Bay area and Sicily's Agrigento district.
Because celestine forms in low-temperature sedimentary environments rather than hot hydrothermal veins, its crystals tend to be delicate and easily damaged, so collectors should handle geode specimens with padded supports rather than bare hands. The mineral's pale blue tone is not always present; colorless, white, and orange forms are also common depending on trace impurities. Strontium extracted from celestine ore supplies fireworks, ceramic magnets, and certain glass formulations, giving an otherwise decorative mineral genuine industrial importance.
How to identify Celestine
Celestine forms tabular to prismatic crystals, often pale blue but also colorless, white, gray, or orange, with a vitreous luster and a white streak. Hardness runs about 3 to 3.5, softer than quartz, and it has distinct cleavage in two directions that yields glassy, stepped surfaces when broken. It reacts only weakly, if at all, with dilute acid, unlike calcite, which fizzes vigorously, offering a useful field test when color alone is ambiguous. Barite is its closest look-alike, distinguished mainly by celestine's lower density.
- Compare the specimen's color, luster, crystal habit, grain size, streak, and locality before confirming.
- Use multiple photos when possible, including a fresh surface and a close view of texture.
Where Celestine is found
Reported from multiple localities worldwide; verify locality against specimen provenance when available.
How much is Celestine worth?
| Entry-level specimen | $2 |
|---|---|
| Typical collector specimen | $20 |
| Premium specimen | $150+ |
Value depends on size, crystal quality, color, locality, rarity, damage, and provenance.
Common uses
- Collector specimens
- Education
- Field identification
- Industrial or lapidary use when suitable
Interesting facts
- Some of the world's largest celestine geodes, found in Ohio, contained crystal-lined cavities big enough for a person to stand inside.
- Strontium extracted from celestine gives fireworks their vivid red color when burned.
- The name celestine derives from the Latin word for heavenly, chosen because early specimens showed a delicate sky-blue tint.
Care & safety
Handle as a collector specimen until hardness, cleavage, and fracture are verified.
Avoid inhaling dust. Do not cut, grind, or polish unknown specimens without eye protection and a proper respirator.
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