Celestine
Celestine is strontium sulphate, SrSO4, 47.70% strontium: hardness 3 to 3.5, density 3.97, pale blue tabular crystals to 45 cm. How to tell it from baryte.
Celestine is strontium sulphate, SrSO4, the Handbook's most common strontium mineral: orthorhombic, hardness 3 to 3.5, density 3.97, colourless to pale blue, in tabular crystals to 45 cm. It is 47.70% strontium by mass. It forms a series with baryte, BaSO4, and density separates them: 3.97 against 4.50.
In short
- Celestine is the IMA name; celestite is the common form of the same word. The September 2026 IMA-CNMNC Master List lists celestine, Sr(SO4), with the status line 1967 s.p. and the USA as type country. The Handbook of Mineralogy derives the name from the Latin for celestial, for its typical bluish colour.
- None of the 176 sheets in this site's reference set has strontium in its formula. Celestine is not in the set either; its sheet was fetched separately. But six sheets in the set name it as an associate, and baryte's names it as its series partner.
- Baryte is the look-alike, and density decides it: the 4.2 line. A 20.00 g piece weighs 14.96 g in water as celestine and 15.56 g as baryte. Under 15.24 g, the reading for density 4.2, is the celestine side.
- The cleavages match baryte's too: perfect on {001}, then {210}, then {010}, in the same order of quality on both sheets, with hardness 3 to 3.5 on both. Colour is a hint, not a test.
- One English locality is on the sheet: Yate, near Bristol. Whether celestine can be confused with quartz is answered on is celestite a quartz.
| Species | Formula | Hardness | Density | Cleavage | 20.00 g piece, weighed in water | Metal by mass |
|---|---|---|---|---|---|---|
| Celestine | SrSO4 | 3 to 3.5 | 3.97 | {001} perfect, {210} good, {010} poor | 14.96 g | 47.70% Sr |
| Baryte | BaSO4 | 3 to 3.5 | 4.50 | {001} perfect, {210} less perfect, {010} imperfect | 15.56 g | 58.84% Ba |
| Anglesite | PbSO4 | 2.5 to 3 | 6.38 | {001} good, {210} distinct, {010} less distinct | 16.87 g | 68.33% Pb |
| Anhydrite | CaSO4 | 3 to 3.5 | 2.98 | {010} perfect, {100} nearly perfect, {001} good to imperfect | 13.29 g | 29.44% Ca |
| Gypsum | CaSO4·2H2O | 1.5 to 2 | 2.317 | {010} perfect, {100} distinct | 11.37 g | 23.28% Ca |
Is it celestine or baryte? The 4.2 line
Celestine and baryte are the same structure with a different metal. The Handbook puts both in the baryte group and says celestine forms a series with barite. Both are orthorhombic and hardness 3 to 3.5. Both cleave perfectly on {001}, then on {210}, then poorly on {010}, and both come colourless, white or pale blue. Their refractive indices differ only in the second decimal: celestine's γ is 1.630 to 1.632, baryte's 1.648. That is no help without a refractometer.
Density does separate them. Celestine's measured density is 3.97, baryte's 4.50, a gap of 13.35%. For a hydrostatic weighing, a piece's weight in water is its weight in air times (1 − 1/density). A 20.00 g piece therefore reads 14.96 g in water as celestine and 15.56 g as baryte. That 0.60 g difference shows plainly on a 0.01 g scale. The rule, which we call the 4.2 line: a density under 4.2, or a 20.00 g piece reading under 15.24 g in water, is on the celestine side. The method is on how to measure specific gravity at home.
The limit of the rule. Because the two form a series, barium-bearing celestine and strontium-bearing baryte fall between 3.97 and 4.50. A reading near 4.2 is a question for an analysis, not a label. Baryte's composition, 58.84% barium, is worked on is baryte toxic.
What is celestine made of? 47.70% strontium
On standard atomic weights, strontium 87.62, sulphur 32.06 and oxygen 15.999, SrSO4 has a formula mass of 183.68 and is 47.70% strontium. As oxides that is SrO 56.41% and SO3 43.59%, which is the Handbook's ideal column exactly. The sheet's real analysis, from Djebel Kebbouch, Tunisia, reads SrO 56.20%, SO3 43.40% and CaO 0.40%. Converted to moles, calcium takes 1.3% of the metal sites.
Strontium is absent from this site's reference set. A regular expression over the header formulas of all 176 sheets finds no Sr in any of them, and the word strontium appears on none. Celestine's own sheet is not one of the 176. It was fetched separately and is used here for celestine's facts only, not counted in any survey. Its Distribution field begins the most common strontium mineral.
Where celestine does appear in the set: as company. It is named in the Association field of six sheets: anhydrite, aragonite, calcite, dolomite, fluorite and gypsum. Baryte's sheet names it as its series partner. Anglesite's sheet mentions it only in the titles of two structure papers. See aragonite and fluorite.
Celestine crystals: tabular, blue and up to 45 cm
The Handbook says well-formed crystals are common, typically thin to thick tabular on {001} with a large {210}. It also records lath-like forms, crystals elongated along [010] or [001] to 45 cm, equant or pyramidal ones, and fibrous, lamellar, earthy and granular masses. Lustre is vitreous, pearly on cleavages.
The colour list is wider than the name suggests: colourless, white, pale blue, pink, pale green, pale brown and black. For blue crystals the sheet records weak pleochroism in indigo-blue, lavender-blue and violet. The sheet does not say what causes the blue, and this page does not guess. The celestine sheet records no fluorescence; its baryte counterpart records that baryte may fluoresce. See fluorescent minerals explained.
At hardness 3 to 3.5 with a perfect cleavage, celestine is scratched by a steel point and splits along {001}. In a crystal tabular on {001}, the broad faces lie parallel to that perfect cleavage. See cleavage or fracture: how to tell.
Where celestine is found, including Yate near Bristol
The sheet gives three settings, each with its own associates. It forms in bedded evaporites with gypsum, anhydrite and sulphur. It forms in cavities in carbonate rocks, precipitated by strontium-bearing ground water or basinal brines, with strontianite, calcite, dolomite, anhydrite, gypsum and fluorite. It also forms in mafic volcaniclastics with analcime, natrolite, hydroxyapophyllite and celadonite. The volcanic setting is why celestine turns up with the zeolites; see which minerals are zeolites.
The Handbook lists only a few localities for fine and large crystals. In the USA these are near Bellwood, Pennsylvania; Crystal Cave at Put-in-Bay on South Bass Island, and Clay Center, Ohio; Cave-in-Rock, Illinois; the Scofield quarry at Maybee, Michigan; and Adamsville, Texas. Outside the USA it names Dundas, Ontario; near Matehuela, San Luis Potosi, and Musquiz and Ramos Arizpe, Coahuila, Mexico; and Girgenti and elsewhere in Sicily. It adds the Konrad mine near Salzgitter, Germany; Yate, near Bristol, England; Bamle, Norway; Jebel Mokattem near Cairo; and Sakoany, near Mahajanga, Madagascar.
The rest of the sulphates are indexed at the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.