How to identify celestite
Five steps to identify celestite (IMA celestine, SrSO4): cleavage, hardness 3 to 3.5, 14.96 g in water for 20 g, a 76° cleavage angle, and indices under 1.633.
To identify celestite, the IMA’s celestine, SrSO4: find one perfect pearly cleavage, check hardness 3 to 3.5, then weigh it. A 20.00 g piece reads 14.96 g in water, baryte 15.56 g. Two finer checks finish it: the {210} cleavages meet at 76.0° (baryte 78.3°), and every celestine refractive index is below 1.633.
In short
- Step 1, day one: look at the break. The Handbook of Mineralogy celestine sheet gives cleavage {001} perfect, {210} good, {010} poor, and a lustre pearly on cleavages. Crystals are typically tabular on {001}, so the broad face is parallel to the perfect cleavage. A flat pearly step on a broken edge is the first sign; glassy shell-like breaks point elsewhere.
- Steps 2 and 3: hardness, then weight. Hardness 3 to 3.5 rules out quartz, at 7, by the test on is celestite a quartz. Then weigh: a 20.00 g piece reads 14.96 g in water as celestine. anhydrite reads 13.29 g, fluorite 13.70 to 13.72 g, baryte 15.56 g, anglesite 16.87 g. The baryte cut-off is on the celestine page.
- Step 4: the 76-degree check. On a cleavage plate parallel to {001}, the two {210} cleavages cross. Worked from each sheet’s cell as 2·arctan(a/2b), they meet at 75.97° in celestine and 78.29° in baryte, 2.32° apart. Positive control: the same cell gives d(210) = 3.294 Å for celestine and 3.445 Å for baryte, matching lines the sheets print.
- Step 5: the 1.634 gap. Celestine’s indices are α 1.619 to 1.622, β 1.622 to 1.624, γ 1.630 to 1.632. Baryte’s are α 1.636, β 1.637, γ 1.648. No celestine reading on its sheet reaches baryte’s lowest, so a refractometer reading below about 1.634 is on the celestine side.
- Documented failure: anglesite at 76.31°. Anglesite, PbSO4, has the same cleavage set and its {210} cleavages meet at 76.31°, only 0.34° from celestine. The angle cannot separate them; weight can, 16.87 g against 14.96 g. Colour separates none of these: the celestine sheet lists seven colours. Dyed material is covered on how to tell if a crystal is dyed.
| Mineral | Hardness | Density (meas.) | 20.00 g in water | Cleavage as printed | Angle between {210} cleavages | Refractive indices | Separates from celestine by |
|---|---|---|---|---|---|---|---|
| Celestine (celestite) | 3 to 3.5 | 3.97 | 14.96 g | {001} perfect; {210} good; {010} poor | 75.97° | α 1.619–1.622; γ 1.630–1.632 | — |
| Baryte | 3 to 3.5 | 4.50 | 15.56 g | {001} perfect; {210} less perfect; {010} imperfect | 78.29° | α 1.636; γ 1.648 | Weight, angle, index |
| Anglesite | 2.5 to 3 | 6.38 | 16.87 g | {001} good; {210} distinct; {010} less distinct | 76.31° | α 1.877; γ 1.894 | Weight, index; not angle |
| Anhydrite | 3 to 3.5 | 2.98 | 13.29 g | {010} perfect; {100} nearly perfect; {001} good to imperfect; pseudocubic fragments | No {210} cleavage | α 1.567–1.574; γ 1.609–1.618 | Weight, fragment shape, index |
| Fluorite | 4 | 3.175 to 3.184 | 13.70 to 13.72 g | {111} perfect | No {210} cleavage | n 1.433–1.448, isotropic | Weight, cleavage, index |
| Calcite | 3 | 2.7102 | 12.62 g | {10-11} perfect | No {210} cleavage | ω 1.658; ε 1.486 | Weight, index |
| Quartz | 7 | 2.65 | 12.45 g | Rarely observable | — | ω 1.544; ε 1.553 | Hardness, weight |
| Gypsum | 1.5 to 2 | 2.317 | 11.37 g | {010} perfect; {100} distinct; {011} | — | α 1.521; γ 1.530 | Hardness, weight |
How do you identify celestite, step by step?
Five readings, in order; stop when one fails. The numbers are from the Handbook of Mineralogy sheets for celestine and its look-alikes, as printed.
- Look at a broken edge or the base. One perfect cleavage, pearly, parallel to the broad face of a tabular crystal: consistent with celestine. How to read a break is on cleavage or fracture.
- Test hardness on an unseen spot. 3 to 3.5 on the sheet. The steel-point reading against quartz is on is celestite a quartz; the method is on how to test mineral hardness properly.
- Weigh it in water. 20.00 g reads 14.96 g as celestine; scale any other weight in proportion. Method on how to measure specific gravity at home.
- Measure the cleavage angle on a {001} cleavage plate where both {210} cleavages show: about 76° (104° on the obtuse side) for celestine, about 78° for baryte.
- Read the refractive index on a polished or clean cleavage face: every celestine index on the sheet is between 1.619 and 1.632.
The finish state. A piece that passes all five is celestine on its sheet’s numbers. A weight between 14.96 g and 15.56 g is the zone where the Handbook says celestine forms a series with baryte; there, a chemical analysis decides, not a step on this list.
What is the 76-degree check?
An angle worked from each sheet’s cell. Celestine and baryte are both orthorhombic, space group Pnma, and both cleave on {001} and {210}. The angle between the (210) and (2-10) cleavages is 2·arctan(a/2b). With celestine’s a = 8.359 and b = 5.352 that is 75.97°; with baryte’s a = 8.884 and b = 5.457, 78.29°; with anglesite’s a = 8.482 and b = 5.398, 76.31°.
The positive control. The same indexing gives d(210) = 1/√((2/a)² + (1/b)²): 3.294 Å for celestine, 3.445 Å for baryte and 3.335 Å for anglesite. The sheets print X-ray lines at 3.295, 3.445 and 3.333, so the cell and the {210} label describe the same planes. The angle is a calculation from printed data, not a measurement this page made.
Its limit. 2.32° between celestine and baryte needs a contact goniometer or a measured photograph of a clean cleavage plate, and the series between them, recorded on both sheets, will move the angle with composition. Anglesite sits 0.34° from celestine, so the angle does not separate those two.
Why does a refractometer separate celestine from baryte?
Because their ranges do not touch on the sheets. The celestine sheet prints α 1.619 to 1.622, β 1.622 to 1.624 and γ 1.630 to 1.632. The baryte sheet prints α 1.636, β 1.637 and γ 1.648. The highest celestine figure, 1.632, is 0.004 below the lowest baryte figure, 1.636. Name it the 1.634 gap: on a refractometer, readings that stay below 1.634 are on the celestine side.
What it does not cover. These are the printed figures for the specimens the sheets describe. Material between the two in composition will read between them. Anhydrite, α 1.567 to 1.574, γ 1.609 to 1.618, also reads below 1.634, but it weighs 13.29 g against 14.96 g and its cleavages give pseudocubic fragments rather than a 76° rhomb. Anglesite reads far higher, 1.877 to 1.894.
What does celestite look like, and what colour is it?
Usually tabular, often blue, never only blue. The sheet says well-formed crystals are common, typically thin to thick tabular on {001} with a large {210}, also lath-like, elongated along [010] or [001] to 45 cm, equant or pyramidal, and fibrous, lamellar, earthy or massive granular. Its colours are colourless, white, pale blue, pink, pale green, pale brown and black. The name is from the Latin for celestial, for the typical bluish colour.
Is it real? Nothing in the five steps depends on colour, which is why they work on a white or grey piece as well as a blue one. This page makes no claim about dyed or treated celestine; the general checks are on how to tell if a crystal is dyed and how to tell if a crystal is fake. The species facts are on celestine, the baryte facts on baryte, and the general method on how to identify a mineral specimen. More are under the collecting guides. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.