How to identify Quartz

To correctly identify Quartz (Quartz), check each of these features in order. Many rocks and minerals look alike, so cross-reference multiple properties before deciding.

Step-by-step identification

1. 1

   Color

   Overall color and any zoning or banding

   Highly variable; colorless, white, gray, purple (amethyst), yellow (citrine), pink (rose quartz), brown (smoky quartz), green, black. Often transparent to translucent.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) to greasy.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Typically smooth to slightly rough on crystal faces; conchoidal fracture surfaces are smooth and curved.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Hexagonal prisms terminated by hexagonal pyramids. Often found as anhedral (irregular) grains in rocks or as massive aggregates. Well-formed crystals are common in vugs and veins.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None. Quartz exhibits conchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Igneous rocks (granite, rhyolite, pegmatite), metamorphic rocks (gneiss, schist, quartzite), sedimentary rocks (sandstone, chert), hydrothermal veins, geodes, and as detrital grains in sediments.

Key Facts

Hardness

7 on the Mohs scale

Specific Gravity

2.65 g/cm³

Crystal System

Trigonal (low quartz) or Hexagonal (high quartz)

Color

Colorless, white, gray, purple, yellow, pink, brown, green, black

Luster

Vitreous to greasy

Transparency

Transparent to opaque

Fracture

Conchoidal

Cleavage

None

Composition

Silicon dioxide (SiO2)

Physical characteristics

• Crystal Habit: Prismatic, massive, granular, cryptocrystalline (e.g., chalcedony). Well-formed crystals are typically hexagonal prisms terminated by rhombohedra (often appearing as hexagonal pyramids).
• Cleavage Type: Absent. Quartz lacks cleavage.
• Fracture Type: Conchoidal (shell-like), producing smooth, curved surfaces with sharp edges.
• Tenacity: Brittle
• Luster Type: Vitreous (glassy) on crystal faces; greasy on massive or fractured surfaces.

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