# Quartz vs. corundum: how to tell them apart

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

## Summary

Quartz and corundum can both form glassy, colorful crystals without true cleavage. Corundum is substantially harder, denser, and commonly barrel-shaped or tabular; quartz commonly forms six-sided prisms with pyramidal terminations.

## Bottom line

Use crystal form and provenance first. Corundum scratches quartz, but do not perform destructive scratch tests on attractive or potentially valuable crystals; uncertain gem material belongs with a qualified gemologist.

## Side-by-side evidence

- Hardness: Quartz — Mohs 7 Corundum — Mohs 9 Interpretation — Corundum scratches quartz, but mutual scratching can permanently damage both.
- Habit: Quartz — Commonly six-sided prisms with pyramidal terminations Corundum — Commonly barrel-shaped, prismatic, tabular, or rounded Interpretation — Well-preserved natural faces can separate typical crystals nondestructively.
- Breakage: Quartz — No cleavage; conchoidal fracture Corundum — No true cleavage; parting may create planar breaks Interpretation — Flat parting in corundum can be mistaken for cleavage.
- Density: Quartz — Specific gravity about 2.65 Corundum — Specific gravity near 4 Interpretation — Corundum feels heavier than quartz of equal compact volume.

## Field sequence

1. Document crystal shape and host rock before removing or cleaning anything.
2. Inspect natural faces and existing breaks with a hand lens.
3. Compare heft only with similarly sized compact specimens.
4. Seek gemological testing instead of scratching a plausible ruby or sapphire.

## Limits and cautions

- Color does not distinguish amethyst, ruby, sapphire, or treated material reliably.
- Synthetic corundum and manufactured glass may occur in jewelry or industrial debris.
- Field tests cannot establish natural origin, treatment, gem quality, or value.

## Frequently asked questions

### Can corundum scratch quartz?

Yes. Mohs 9 corundum scratches Mohs 7 quartz, but this is not an appropriate test for a potentially valuable specimen.

### Is every red corundum ruby?

Ruby is the red gem variety of corundum, but color quality, natural origin, treatments, and value require professional evaluation.

### Can quartz look like sapphire?

Blue quartz and manufactured materials can resemble sapphire in color. Crystal form, density, optical properties, and laboratory tests provide stronger evidence.

## Related identification guides

- Quartz: https://lithomap.app/resources/mineral-identification/quartz
- Corundum: https://lithomap.app/resources/mineral-identification/corundum

## 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
- Corundum and Its Occurrence and Distribution in the United States — U.S. Geological Survey: https://www.usgs.gov/publications/corundum-and-its-occurrence-and-distribution-united-states-a-revised-and-enlarged

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