How to identify Quartz

To correctly identify Quartz (SiO 2), 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

   Colorless, white, milky, 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

   Smooth to slightly rough, depending on crystal habit and fracture.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Typically forms hexagonal prisms terminating with hexagonal pyramids. Can also be massive, granular, cryptocrystalline (e.g., chalcedony), or botryoidal.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None. Exhibits conchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

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

Key Facts

Hardness

7 (Mohs scale)

Specific Gravity

2.65 g/cm³

Crystal System

Trigonal (often appears hexagonal)

Color

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

Luster

Vitreous to greasy

Transparency

Transparent to opaque

Fracture

Conchoidal

Cleavage

None

Composition

Silicon dioxide (SiO2)

Physical characteristics

• Crystal Habit: Prismatic (hexagonal), massive, granular, cryptocrystalline, drusy, botryoidal
• Cleavage Type: None
• Fracture Type: Conchoidal
• Tenacity: Brittle
• Luster Type: Vitreous (glassy) to greasy

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