How to identify Quartzite

To correctly identify Quartzite (Metamorphic rock, primarily quartz (SiO2)), 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

   Typically white to light gray, but can be pink, red, purple, yellow, green, or blue due to impurities (e.g., iron oxides for reds/pinks, chlorite for greens).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) to greasy on freshly broken surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Granular, sugary, and often interlocking. The grains are typically equigranular. Unlike sandstone, individual sand grains are not easily discernible, and the rock breaks across the grains.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Microcrystalline to macrocrystalline interlocking quartz grains, often anhedral (lacking well-formed crystal faces).

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None. Quartz itself lacks cleavage, and the interlocking nature of quartzite prevents macroscopic cleavage planes. It exhibits conchoidal to subconchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Formed in regions of regional metamorphism (e.g., mountain belts, cratonic shields) or contact metamorphism (adjacent to igneous intrusions) where quartz-rich sandstones are subjected to high temperatures and pressures.

Key Facts

Hardness

7 on the Mohs scale

Specific Gravity

2.65 g/cm³ (for pure quartz)

Crystal System

Trigonal (for quartz component)

Color

White, gray, pink, red, purple, yellow, green, blue

Luster

Vitreous to greasy

Transparency

Translucent to opaque

Fracture

Conchoidal to subconchoidal, irregular

Cleavage

None

Composition

Primarily quartz (SiO2), typically >90% quartz. Minor accessory minerals may include feldspar, mica, garnet, zircon, rutile, magnetite, and iron oxides.

Physical characteristics

• Crystal Habit: Anhedral, interlocking granular mosaic of quartz crystals.
• Cleavage Type: Absent.
• Fracture Type: Conchoidal to subconchoidal, irregular.
• Tenacity: Brittle.
• Luster Type: Vitreous (glassy) to greasy.

Explore Quartzite