sulfates
Celestine
Sr(SO4)
- Also known as
- celestite
- Crystal system
- orthorhombic
- Hardness
- 3–3.5 on the Mohs scale
- Lustre
- vitreous
- Colour
- Pale sky blue, white, colourless
- Where it forms
- In sedimentary rocks, particularly in cavities in limestone and in evaporite sequences, where strontium-bearing water was concentrated.
- Chiefly from
- MadagascarPut-in-Bay, Ohio, United StatesSicilyPoland
Why it is that colour
The gentle blue is not well explained by a simple impurity and is generally attributed to colour centres, possibly involving trapped sulfur species.
Safety
Safe to handle. Strontium sulfate is insoluble and stable. The geodes are fragile and the crystals chip easily.
Where it comes from
Madagascan geodes dominate the decorative market and are extracted by small-scale miners under the same informal conditions as that country’s other gem production. The largest known geode, at Put-in-Bay in Ohio, is about ten metres across and is open to visitors.
Historical use
The main ore of strontium, which was used in cathode ray tube glass and in red fireworks and flares. Demand fell sharply when televisions stopped using tubes.
Recorded as history and attributed where possible. That a stone was used for something establishes that people used it, not that it worked.
What is attributed to it, and since when
Named in 1799 for its sky colour, from the Latin caelestis. It has no traditional history at all. The strong modern association with angels is a straightforward derivation from the name and is recent.
Described, not endorsed. Dating a claim is not the same as assessing it — but an association that first appears in a book published in 1985 is not an ancient inheritance, whatever the label says. A sincere account of feeling better is compatible with the stone doing nothing — see the placebo effect.
Worth knowing
Celestine is a clean example of a meaning derived from a name rather than from anything about the material. It was called celestine in 1799 because it is sky blue. Two centuries later it is sold as the stone for contacting angels, and the chain of reasoning from one to the other is visible in a single step.
The red of a firework flare is strontium, and strontium mostly came from this mineral. It is a better fact than the angels.
Identity checked against IMA-CNMNC master list, June 2025.