# How to identify celestite

Canonical page: https://lithomap.app/resources/mineral-identification/celestite
Last reviewed: September 17, 2026
Page purpose: Original LithoMap mineral identification reference for field observations, search systems, and language models.
Classification: Strontium sulfate · SrSO₄

## Summary

Celestite is a strontium sulfate mineral commonly found as pale blue, white, or colorless tabular crystals with high density, white streak, good cleavage, and hardness near 3 to 3.5.

## Quick identification clues

- Often pale sky blue but may be white or colorless
- Heavy for a nonmetallic mineral
- Mohs hardness about 3 to 3.5
- Tabular, bladed, prismatic, granular, or fibrous habits

## Composition and classification

Celestite is strontium sulfate and forms a solid-solution relationship with barite in some natural materials. Color may come from defects or impurities and is not a reliable measure of composition.

## Appearance

Crystals commonly form transparent to translucent tablets, blades, or prisms with vitreous to pearly luster. It also occurs fibrous, granular, or massive.

Although pale blue is memorable, many specimens are white, gray, yellowish, reddish, or colorless and can resemble barite, calcite, or gypsum.

## Identification tests

- Density: High; specific gravity commonly near 4. Heavier than calcite or gypsum but often slightly lighter than barite.
- Hardness: About 3 to 3.5. Scratched by steel and overlaps barite and calcite.
- Cleavage: Good to perfect in more than one direction. Produces flat reflective breaks but is not decisive against barite.
- Streak: White. Consistent but shared by many pale minerals.

## Common lookalikes

- Barite: Usually slightly denser; visual separation can be unreliable without measured density or analysis.
- Calcite: Much lighter and reacts vigorously with dilute acid.
- Gypsum: Much softer at Mohs 2 and lighter.

## Direct side-by-side comparisons

- Celestite vs. barite — https://lithomap.app/resources/mineral-identification/compare/celestite-vs-barite

## Most relevant related guides

- Barite — https://lithomap.app/resources/mineral-identification/barite
- Calcite — https://lithomap.app/resources/mineral-identification/calcite
- Gypsum — https://lithomap.app/resources/mineral-identification/gypsum
- Apatite — https://lithomap.app/resources/mineral-identification/apatite

## Formation

Celestite forms in sedimentary evaporite and carbonate environments, in cavities and geodes, and through low-temperature hydrothermal processes.

It may occur with gypsum, anhydrite, calcite, sulfur, halite, fluorite, or barite.

## Occurrence and geologic setting

Celestite occurs in sedimentary basins, evaporite sequences, carbonate cavities, and some geodes, with important deposits in several parts of the world and scattered U.S. occurrences.

Blue color alone does not establish celestite, and a hand specimen may require specific-gravity or analytical confirmation.

## Uses and significance

Celestite is the principal mineral source of strontium, used in ceramics, glass, ferrite magnets, pyrotechnics, metallurgy, and other chemical applications.

## Field safety and limitations

- Do not perform flame tests outside a controlled laboratory.
- Compare measured volume and mass rather than subjective heft when possible.
- Avoid dust and do not ingest unknown sulfate minerals.

## Authoritative sources

- Strontium Statistics and Information — U.S. Geological Survey: https://www.usgs.gov/centers/national-minerals-information-center/strontium-statistics-and-information
- Minerals and their physical properties — U.S. National Park Service: https://www.nps.gov/subjects/geology/minerals.htm
- Mohs Hardness Scale — U.S. National Park Service: https://www.nps.gov/articles/mohs-hardness-scale.htm
- Natural Gemstones: Mineral Gemstones — U.S. Geological Survey: https://pubs.usgs.gov/gip/gemstones/mineral.html

## Specimen photograph

- Image: https://lithomap.app/_delivery/identification/minerals/celestite.webp
- Description: Cluster of pale, faintly blue celestite crystals from Lampasas County, Texas
- Creator: Dexter Perkins
- License: CC0 1.0 — https://creativecommons.org/publicdomain/zero/1.0/
- Source record: https://commons.wikimedia.org/wiki/File:Celestite_%28GeoDIL_number_-_601%29.jpg

This reference supports preliminary field identification. It is not a laboratory determination, appraisal, hazard assessment, proof of origin, or statement of land ownership, legal access, or collecting permission.