Is celestite the same as blue calcite?
Is celestite blue calcite? No: SrSO4 against CaCO3, two species. Hardness overlaps, 3 to 3.5 vs 3; weight and cleavage decide: celestite is 1.46 times denser.
No. Celestite, the IMA’s celestine, is strontium sulphate, SrSO4; blue calcite is calcite, calcium carbonate, CaCO3, that is blue. Hardness overlaps, 3 to 3.5 against 3, so weight decides: density 3.97 against 2.7102, and a 20.00 g piece reads 14.96 g against 12.62 g in water.
In short
- Two species, two chemical classes. On the September 2026 IMA-CNMNC Master List celestine is Sr(SO4), a sulphate; calcite is Ca(CO3), a carbonate. The Handbook of Mineralogy sheets make celestine orthorhombic, hardness 3 to 3.5, density 3.97, and calcite hexagonal, hardness 3, density 2.7102. Celestite is the common form of celestine’s name. No fetched source defines “blue calcite” as a trade name, so this page reads it as calcite that is blue.
- The 1.46 heft rule. At 3.97 against 2.7102, celestine weighs 1.46 times as much as calcite of the same size: a 1 cm cube is 3.97 g against 2.71 g, and 20.00 g fills 5.04 cm3 against 7.38 cm3. Two pieces that look the same size, one clearly heavier in the hand, point to celestine.
- The 14.2 g line. In water, a 20.00 g piece reads 14.96 g as celestine and 12.62 g as calcite. The International Gem Society lets calcite reach specific gravity 2.94, which reads 13.20 g. Halfway in density between that 2.94 and celestine’s 3.97 is 3.455, a reading of 14.2 g: below it, the calcite side; above it, not calcite.
- Count the perfect cleavages. The celestine sheet prints one perfect cleavage, {001}, plus a good {210} and a poor {010}; the calcite sheet prints the {10-11} rhombohedron, perfect, which the International Gem Society describes as 3 directions. Celestine splits into plates parallel to the broad face; calcite breaks into rhombs.
- Documented failure: fizz is not proof. Calcite effervesces in dilute hydrochloric acid, and Perkins et al., Mineralogy, section 3.9 (LibreTexts) calls the reaction diagnostic for calcite. The same section says strontianite effervesces too, to a different degree, and strontianite is one of celestine’s own associates. It reads 14.68 g in water, on the celestine side of the line. This page gives no acid procedure.
| Test | Celestite (celestine) | Calcite | Gap | Use it when | Wrong for |
|---|---|---|---|---|---|
| Formula; class | SrSO4; sulphate | CaCO3; carbonate | — | — | — |
| Hardness (Mohs) | 3–3.5 | 3 | None | Never for this pair | Every piece: the ranges overlap |
| Density | 3.97 (IGS 3.97–4.00) | 2.7102 (IGS 2.71 to 2.94) | 1.46 times by volume | Any solid single-mineral piece | Matrix, mixed celestine–calcite pieces |
| 20.00 g in water | 14.96 g | 12.62 g (13.20 g at 2.94) | 2.34 g (1.76 g) | A 0.1 g scale is enough | Pieces with matrix or cavities |
| Perfect cleavages | 1: {001}; also {210} good, {010} poor | 3: the {10-11} rhombohedron | 1 against 3 | Crystals and broken edges | Massive, tumbled or polished pieces |
| Break shape | Plates parallel to the broad tabular face | Rhombs | — | A chipped edge | Fibrous or earthy material |
| Optic class; birefringence | Biaxial (+); 0.008–0.013 (IGS 0.009–0.012) | Uniaxial (–); 0.172 (IGS 0.172–0.190) | 13 to 21.5 times | Clear material over a printed line | Translucent to opaque pieces |
| Refractive indices | α 1.619–1.622; β 1.622–1.624; γ 1.630–1.632 | ω 1.658; ε 1.486 | ω 0.026 above celestine’s highest | A refractometer and a polished face | Rough material |
| Colour as printed | Colorless, white, pale blue, pink, pale green, pale brown, black | Colorless or white, also gray, yellow, green, many other colors from included minerals (IGS adds blue) | Both can be blue | Never | Every piece |
| Luminescence as printed | None on the sheet; white or blue in the specimen records on the UV page | May fluoresce red, blue, yellow and other colours, SW and LW | Can be identical | Never | Every piece |
| Reaction to dilute HCl | No carbonate in the formula | Effervesces; diagnostic (Perkins) | — | Not given here | Strontianite also effervesces |
Is celestite blue calcite? Two different minerals
Celestite and blue calcite are different species: strontium sulphate against calcium carbonate. The September 2026 IMA list has a row for celestine, Sr(SO4), status A, 1967 s.p., USA, and one for calcite, Ca(CO3), grandfathered, 1836; a script over the list finds no line containing celestite or blue calcite. Celestite is the common form of celestine’s name. The Handbook celestine sheet puts it in the baryte group, orthorhombic; the Handbook calcite sheet puts calcite in the calcite group, hexagonal.
What “blue calcite” means here. No source fetched for this page defines blue calcite as a trade name, so this page treats it as calcite that is blue. The calcite sheet’s colour line does not name blue: it reads colorless or white, also gray, yellow, green, many other colors from included minerals. The International Gem Society calcite article does list blue among calcite’s colours. The celestine sheet prints pale blue among seven colours, and takes the name from the Latin for celestial, for the typical bluish colour.
They are found together. The celestine sheet names calcite among its associates in cavities in carbonate rocks, and the calcite sheet names celestine in low-temperature veins. A blue cluster can be one, the other, or both; the species pages are celestine and calcite.
The 1.46 heft rule: why celestite feels heavier than calcite
Size for size, celestite weighs about one and a half times as much as calcite. The sheets give a measured density of 3.97 for celestine and 2.7102 for calcite. The ratio is 1.465. A 1 cm cube would weigh 3.97 g as celestine and 2.71 g as calcite; 20.00 g of celestine fills 5.04 cm3, 20.00 g of calcite 7.38 cm3. Picked up together, two single-mineral pieces of the same size are not close.
The 14.2 g line, for a scale. Weighed suspended in water, a 20.00 g piece reads 14.96 g as celestine and 12.62 g as calcite, the figures how to identify celestite and how to tell calcite from quartz use. The International Gem Society calcite article gives calcite a specific gravity of 2.71 (pure) to 2.94, and the International Gem Society celestite article gives celestite 3.97 to 4.00. At 2.94 a 20.00 g calcite reads 13.20 g, so the gap narrows from 2.34 g to 1.76 g. Halfway between 2.94 and 3.97 is 3.455, which reads 14.21 g: below 14.2 g is the calcite side of both sources. A 0.1 g scale resolves it; the method is on how to measure specific gravity at home.
Documented failure: strontianite. Strontium carbonate, SrCO3, is on the celestine sheet’s associate list. Its sheet gives density 3.76, so a 20.00 g piece reads 14.68 g, on the celestine side of the line, and as a carbonate it can fizz. Its colour list has no blue, but a heavy piece that fizzes is not settled by either test alone; the strontianite facts are on strontianite.
Count the perfect cleavages: one for celestite, three for calcite
Celestite has one perfect cleavage; calcite has three, at the faces of a rhomb. The celestine sheet reads: on {001}, perfect; on {210}, good; on {010}, poor; fracture uneven. The calcite sheet reads {10-11}, perfect, the rhombohedron. The International Gem Society celestite article writes celestite’s as perfect 1 direction, good 1 direction; the International Gem Society calcite article writes calcite’s as perfect rhombohedral, 3 directions.
What it looks like. Celestite crystals are typically tabular on {001}, so the perfect cleavage lies parallel to the broad face and a chip lifts off as a flat, pearly plate. Calcite breaks along three equal planes, none at right angles, into rhombs. The angle between celestite’s two {210} cleavages is the separate test on how to identify celestite; how to read a break is on cleavage or fracture.
Clear pieces also double. Calcite’s indices, ω 1.658 and ε 1.486, differ by 0.172; celestine’s highest and lowest differ by 0.008 to 0.013, so calcite’s birefringence is 13 to 21.5 times larger. A clear calcite doubles a line seen through it; why, and how to look, is on how to tell calcite from quartz. Calcite’s ω of 1.658 also sits 0.026 above celestine’s highest index, 1.632.
Which test should you use? What each one is wrong for
Use weight for a solid piece, cleavage for a crystal, and never hardness, colour or UV. Hardness is 3 to 3.5 against 3, so a steel point marks both; the method is still on how to test mineral hardness properly. Colour is no use: both sheets allow pale or white material, and the IGS calcite article lists blue. Under a lamp both can glow, and specimen records log the calcite beside celestine with the same response; that ledger is on is celestite UV reactive.
Where the good tests fail. Weight is wrong for a piece on matrix or with cavities, and for a piece that is both minerals, which the two sheets’ association lists make possible. The cleavage count is wrong for massive, tumbled or polished material that shows no break. Doubling needs clear material. Whether a piece is dyed is a separate question, covered on how to tell if a crystal is dyed; how easily celestite breaks is on is celestite fragile, and the quartz question on is celestite a quartz.
Acid is the textbook test, and this page does not use it. Perkins et al., Mineralogy, section 3.9 (LibreTexts) calls the reaction to dilute (5%) hydrochloric acid diagnostic for calcite; celestine, SrSO4, has no carbonate in its formula. Neither Handbook sheet mentions effervescence. This page gives no acid procedure; any hazard question goes to toxic minerals in a collection, and nothing here is safety advice. More guides are in the collecting guides. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.