LithoMap

Mineral identification comparison

Quartz vs. feldspar: how to tell them apart

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.

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Cluster of transparent quartz crystals from Pennsylvania
QuartzSilicate mineral · SiO₂Photo: Lunamothminerals · CC BY 4.0
Pink potassium feldspar hand specimen showing blocky cleavage
FeldsparSilicate mineral groupPhoto: James St. John · CC BY 2.0
Quick answer

The most useful distinction

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

Quartz and Feldspar comparison table

PropertyQuartzFeldsparHow to use it
CleavageAbsent; breaks by conchoidal or irregular fractureTwo good cleavage directions, commonly near 90°Repeated planar breakage is the strongest field distinction.
HardnessMohs 7About Mohs 6Both can scratch glass, so hardness alone rarely resolves the pair.
Luster and clarityCommonly glassy and translucent, with gray, clear, or smoky grainsCommonly pearly to glassy and white, pink, cream, or gray; alteration may make it cloudyAppearance is useful only after cleavage is checked.
Surface markingsNatural faces may show horizontal growth lines but not feldspar twinning striationsPlagioclase cleavage faces may show fine parallel striations; potassium feldspar may show other twinningStriations can confirm plagioclase when visible with a hand lens.
Field sequence

A practical identification sequence

  1. 1

    Rotate the grain under light and search for repeated flat cleavage surfaces.

  2. 2

    Check whether two planar directions meet at approximately a right angle.

  3. 3

    Look with a hand lens for fine parallel striations on a possible plagioclase face.

  4. 4

    Use hardness, color, and the enclosing rock only as supporting evidence.

Limits and cautions

Where the distinction gets difficult

  • 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.

Use several independent observations. This comparison supports preliminary field identification, not laboratory confirmation, appraisal, proof of origin, or collecting permission.

Common questions

Quartz vs. feldspar FAQ

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.

Source basis

Authoritative sources

LithoMap wrote this comparison in original language from the physical properties and geological concepts supported by these public scientific references.

Editorial review: September 17, 2026.

Resolve another lookalike

More mineral comparisons

All mineral guides
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