# Quartz vs. calcite: how to tell them apart

Canonical page: https://lithomap.app/resources/mineral-identification/compare/quartz-vs-calcite
Last reviewed: September 17, 2026
Page purpose: Original LithoMap side-by-side field identification reference for search systems and language models.

## Summary

Quartz and calcite can both be colorless, white, or glassy, but quartz is harder and lacks cleavage while calcite is softer, has rhombohedral cleavage, and reacts with dilute acid.

## Bottom line

Test an inconspicuous fresh surface. Quartz scratches ordinary glass and breaks with curved or irregular fracture; calcite is scratched by a steel point, cleaves into slanted rhombs, and fizzes with dilute acid.

## Side-by-side evidence

- Hardness: Quartz — Mohs 7; readily scratches glass Calcite — Mohs 3; scratched by a copper coin or steel point Interpretation — A careful hardness test separates typical fresh specimens quickly.
- Breakage: Quartz — No cleavage; conchoidal to irregular fracture Calcite — Three perfect cleavage directions not at 90°, commonly forming rhombohedra Interpretation — Use repeated flat surfaces, not one accidental face, to recognize cleavage.
- Acid response: Quartz — No reaction with ordinary dilute hydrochloric acid Calcite — Strong effervescence on a clean calcite surface Interpretation — Acid is highly useful when applied safely and only to an expendable specimen.
- Crystal form: Quartz — Commonly six-sided prisms with pointed terminations Calcite — Commonly rhombohedra, scalenohedra, or cleavage fragments Interpretation — Crystal shape supports an identification when the specimen retains natural faces.

## Field sequence

1. Check whether a clean edge scratches ordinary glass.
2. Inspect several broken surfaces for repeated rhombohedral cleavage or curved fracture.
3. Use a drop of dilute acid on an expendable fresh spot when appropriate.
4. Confirm with crystal habit and the minerals or rocks surrounding the specimen.

## Limits and cautions

- Fine-grained mixtures can contain both minerals and give mixed test results.
- Coatings and weathered surfaces can hide hardness and acid response.
- Do not acid-test finished stone, valuable specimens, fossils, monuments, or protected outcrops.

## Frequently asked questions

### Can calcite scratch glass?

Fresh calcite is much softer than common window glass and should not scratch it. A harder inclusion, grit, or excessive pressure can create a misleading mark.

### Why do quartz and calcite look alike?

Both can grow as transparent or pale crystals with a glassy luster. Their internal structures produce very different hardness, breakage, and acid behavior.

### Does every carbonate mineral fizz strongly?

No. Calcite reacts readily, while dolomite usually reacts weakly unless powdered. Surface coatings and dilute reagents also change the visible response.

## Related identification guides

- Quartz: https://lithomap.app/resources/mineral-identification/quartz
- Calcite: https://lithomap.app/resources/mineral-identification/calcite

## Authoritative sources

- 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

This reference supports preliminary field identification. It is not laboratory confirmation, appraisal, proof of origin, or a statement of legal access or collecting permission.