Celestite (天青石 / Celestite, Celestine)
Celestite is a sulfate mineral characterized by a pale blue color reminiscent of the sky. Discovered in 1781 in Sicily, Italy, it was named after the word celestial, meaning "of the sky." It is particularly famous for the crystal clusters that form in the cavities of sandy marl in Madagascar and is commonly sold in the form of geodes.
Celestite crystals as if they have captured the color of the sky
Basic Information
| English Name | Celestite / Celestine |
|---|---|
| Japanese Name | Ten-seiseki (Celestite) |
| Chemical Composition | SrSO₄ |
| Crystal System | Orthorhombic |
| Hardness | 3–3.5 |
| Specific Gravity | Approx. 4.0 |
Characteristics, Varieties, and Trade Names
Celestite is a type of sulfate mineral; other members of the same group include barite, gypsum, and anglesite. They form solid solutions with each other, and types with intermediate properties also exist.
While it is generally known for its pale blue color, rare colors such as red, orange, and yellow also exist.
- Bicolor Celestite: A type where both blue and white appear within the same crystal.
- Celestite Cat's Eye: A translucent stone that may exhibit a faint, eye-like girasol effect resulting from a collection of fine cleavages.
- Celestial Aquamarine: Pale blue Celestite is sometimes marketed under trade names intended to evoke an association with aquamarine.
Treatments, Similar Stones, and Identification
Because it has perfect cleavage and is very fragile, Madagascar geodes are often coated with cementing material to reinforce the exterior before they are sold. Resin impregnation may also be performed to reinforce fractures.
Strontium-bearing barite looks quite similar. Furthermore, it can be distinguished from calcite by the fact that while Celestite has cleavage in only one direction, calcite has perfect cleavage in three directions.
When Celestite powder is introduced into a flame, it turns the flame red. This is a flame test reaction caused by Sr, which serves as a clue for identification.
Handling Precautions: Due to its low hardness and perfect cleavage, this stone is prone to cracking from impact or drops. Large crystals are particularly rare and fragile, making them better suited for quiet display as collectibles. If using it for jewelry, it is recommended to choose a design where the stone is protected from accidental bumps.