Is celestite fragile?
Yes, by its sheet: celestite (IMA celestine) is brittle, hardness 3 to 3.5, with a perfect {001} cleavage. Of its 11 associates, 4 print a higher hardness.
Yes. The Handbook of Mineralogy sheet for celestine, the IMA name for celestite, SrSO4, records tenacity brittle, hardness 3 to 3.5, a perfect cleavage on {001}, good on {210}, poor on {010}, and uneven fracture. Its typical tabular crystals lie parallel to that perfect cleavage. Of the 11 minerals the sheet names as associates, 4 print a higher hardness.
In short
- What the sheet says. The Handbook of Mineralogy celestine sheet reads: Cleavage: On {001}, perfect; on {210}, good; on {010}, poor. Fracture: Uneven. Tenacity: Brittle. Hardness = 3–3.5. Those are the fields that answer fragile; the word itself is not a sheet term.
- Why a tabular crystal splits flat. The sheet says well-formed crystals are typically thin to thick tabular on {001}. The broad face of such a crystal is therefore the plane of the perfect cleavage, and a split runs parallel to it. Reading a break is on cleavage or fracture.
- The neighbour ledger. The celestine sheet names 11 species as associates. On their own sheets, 4 print a hardness above celestine’s 3.5: fluorite 4, apophyllite (hydroxyapophyllite) 4.5 to 5, natrolite and analcime 5 to 5.5. Four overlap: anhydrite, strontianite, calcite and dolomite. Three sit below 3: gypsum, sulphur and celadonite.
- Documented failure: hardness is not toughness. The sheets print tenacity as its own field. quartz is hardness 7 and still prints Brittle, tough when massive; gypsum at 1.5 to 2 prints Flexible, inelastic. Celestine’s sheet prints Brittle and no exception for massive material, so a higher or lower hardness alone does not answer the question.
- Not covered here. This page gives no care, cleaning or storage method. Identification, including the cleavage-angle and refractive-index checks, is on how to identify celestite; UV behaviour on is celestite UV reactive.
| Species | Setting on the celestine sheet | Hardness as printed | Against celestine 3–3.5 | Tenacity as printed | Cleavage as printed |
|---|---|---|---|---|---|
| Celestine (celestite) | — | 3–3.5 | — | Brittle | {001} perfect; {210} good; {010} poor |
| Gypsum | Evaporites; carbonate cavities | 1.5–2, varies with direction | Softer | Flexible, inelastic | {010} perfect; {100} distinct; {011} |
| Anhydrite | Evaporites; carbonate cavities | 3–3.5 | Overlaps | Brittle | {010} perfect; {100} nearly perfect; {001} good |
| Sulphur | Evaporites | 1.5–2.5 | Softer | Rather brittle to somewhat sectile | Imperfect, on three forms; parting |
| Strontianite | Carbonate cavities | 3.5 | Overlaps | Brittle | {110} nearly perfect; {021} poor |
| Calcite | Carbonate cavities | 3 | Overlaps | Brittle | {10-11} perfect |
| Dolomite | Carbonate cavities | 3.5–4 | Overlaps | Brittle | {10-11} perfect |
| Fluorite | Carbonate cavities | 4 | Harder | Brittle | {111} perfect |
| Analcime | Mafic volcaniclastics | 5–5.5 | Harder | Brittle | Very poor on {100} |
| Natrolite | Mafic volcaniclastics | 5–5.5 | Harder | Brittle | {110} perfect |
| Hydroxyapophyllite | Mafic volcaniclastics | 4.5–5 | Harder | [Brittle.] (bracketed) | Perfect on {001} |
| Celadonite | Mafic volcaniclastics | ~2 | Softer | Friable to unctuous | {001} perfect |
How fragile is celestite? The sheet’s three answers
Brittle, soft, and with one perfect cleavage. Celestine, Sr(SO4) on the September 2026 IMA list, is the species collectors call celestite. Its Handbook of Mineralogy sheet answers the question in three separate fields. Tenacity: brittle. Hardness: 3 to 3.5 on the Mohs scale. Cleavage: on {001}, perfect; on {210}, good; on {010}, poor, with an uneven fracture where it breaks across them.
What each one means on the specimen. Hardness is the scratch reading; the method is on how to test mineral hardness properly. Tenacity is how the sheet records the way a mineral gives, with words such as brittle, sectile or flexible. Cleavage gives the planes it prefers to part on. The sheet calls well-formed crystals common, typically thin to thick tabular on {001} and up to 45 cm, so on most crystals the large flat face is parallel to the perfect cleavage.
The boundary. Fragile here means mechanical. The sheet says nothing about water, light or heat damage, and this page adds nothing on those. The blue colour is discussed on celestine.
Is celestite softer than the minerals it grows with? The neighbour ledger
Against its own associates, it sits in the middle. The celestine sheet names 11 species in its Association field, in three settings: gypsum, anhydrite and sulphur in bedded evaporites; strontianite, calcite, dolomite, anhydrite, gypsum and fluorite in cavities in carbonate rocks; and analcime, natrolite, hydroxyapophyllite and celadonite in mafic volcaniclastic rocks. A script read each species’ own Handbook sheet. Four print a hardness above 3.5, four overlap 3 to 3.5, and three print a hardness below 3.
By setting. In the evaporite group none of the three is harder. In the carbonate-cavity group, fluorite at 4 is harder, and dolomite at 3.5 to 4 reaches above celestine’s range. In the volcanic group, three of the four are harder: hydroxyapophyllite 4.5 to 5, natrolite and analcime 5 to 5.5. Hydroxyapophyllite-(K) is the IMA name for the species the celestine sheet calls hydroxyapophyllite. This is a reading of printed numbers, not a handling rule.
Its series partner. baryte prints the same hardness, 3 to 3.5, the same tenacity, brittle, and a perfect {001} cleavage, so nothing on the two sheets makes one more fragile than the other. Telling them apart is on how to identify celestite.
Why hardness alone does not answer fragile
Because the sheets print tenacity separately, and the two do not track each other. Quartz, hardness 7, prints Tenacity: Brittle, tough when massive. Gypsum, hardness 1.5 to 2, prints Flexible, inelastic. Among celestine’s 11 associates, the brittle ones run from calcite at 3 to analcime and natrolite at 5 to 5.5, while the softest three print three different tenacities: flexible, rather brittle to somewhat sectile, and friable to unctuous.
A second limit: some entries are inferred. The hydroxyapophyllite sheet prints its tenacity as [Brittle.] in square brackets and its fracture as [Uneven], which it says is by analogy to fluorapophyllite. A bracketed field is the sheet’s inference, not a measurement, and the ledger above marks it so.
What celestine’s sheet adds. Unlike quartz, celestine prints no tougher form: its entry is Brittle with no exception for massive, fibrous or granular material. How a perfect cleavage decides the way a fluorite breaks is on why did my fluorite break, and the quartz comparison is on is celestite a quartz. 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.