# Quartz vs. feldspar: how to tell them apart

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

## Summary

Quartz and feldspar are abundant light-colored rock-forming minerals. Quartz lacks cleavage and commonly looks glassy or irregular; feldspar has two good cleavage directions and often appears blocky, pearly, or slightly cloudy.

## Bottom line

Study how the grain ends. Quartz usually has curved or irregular broken surfaces with no repeated flat direction; feldspar commonly shows two recurring cleavage planes that meet near 90 degrees.

## Side-by-side evidence

- Cleavage: Quartz — Absent; breaks by conchoidal or irregular fracture Feldspar — Two good cleavage directions, commonly near 90° Interpretation — Repeated planar breakage is the strongest field distinction.
- Hardness: Quartz — Mohs 7 Feldspar — About Mohs 6 Interpretation — Both can scratch glass, so hardness alone rarely resolves the pair.
- Luster and clarity: Quartz — Commonly glassy and translucent, with gray, clear, or smoky grains Feldspar — Commonly pearly to glassy and white, pink, cream, or gray; alteration may make it cloudy Interpretation — Appearance is useful only after cleavage is checked.
- Surface markings: Quartz — Natural faces may show horizontal growth lines but not feldspar twinning striations Feldspar — Plagioclase cleavage faces may show fine parallel striations; potassium feldspar may show other twinning Interpretation — Striations can confirm plagioclase when visible with a hand lens.

## Field sequence

1. Rotate the grain under light and search for repeated flat cleavage surfaces.
2. Check whether two planar directions meet at approximately a right angle.
3. Look with a hand lens for fine parallel striations on a possible plagioclase face.
4. Use hardness, color, and the enclosing rock only as supporting evidence.

## Limits and cautions

- Tiny grains in granite may not expose enough surface to show cleavage clearly.
- Weathered feldspar can look chalky or clay-like, while iron staining changes either mineral’s color.
- “Feldspar” is a mineral group; precise species identification may require optical or chemical analysis.

## Frequently asked questions

### Is the clear mineral in granite always quartz?

Often, but not always. Some feldspar is translucent, so cleavage and grain shape should be checked rather than relying on clarity.

### Can feldspar scratch glass?

Yes. Most feldspar is about Mohs 6 and can scratch common glass, so a glass test does not prove a grain is quartz.

### Why is feldspar commonly pink?

Some potassium feldspar is pink, salmon, or reddish, but many feldspars are white, cream, gray, green, or nearly colorless. Color is not diagnostic by itself.

## Related identification guides

- Quartz: https://lithomap.app/resources/mineral-identification/quartz
- Feldspar: https://lithomap.app/resources/mineral-identification/feldspar

## 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.