How to identify Quartzite

To correctly identify Quartzite (Metamorphic rock (Quartzite)), 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, yellow, green, or blue due to impurities (e.g., iron oxides, chlorite, mica).

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

   Granular, sugary, or massive. The grains are tightly interlocked and often not visible to the naked eye. Non-foliated, though relict bedding or cross-bedding from the protolith sandstone may occasionally be preserved.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Anhedral, interlocking mosaic of quartz crystals. Individual crystals are typically microscopic to macroscopic, forming a dense, compact mass.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None. Quartzite breaks with a conchoidal fracture, cutting across the quartz grains, unlike sandstone which breaks around the grains.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Formed in regional metamorphic settings associated with mountain-building events (orogenesis) or deep burial. Found in ancient cratonic shields, fold-and-thrust belts, and areas that have undergone significant tectonic compression and heating.

Key Facts

Hardness

7 on the Mohs scale

Specific Gravity

2.65 g/cm³

Crystal System

Trigonal (for quartz, the primary mineral)

Color

Typically white or light gray; can be pink, red, yellow, green, or blue due to impurities.

Luster

Vitreous (glassy) to greasy.

Transparency

Translucent to opaque.

Fracture

Conchoidal to subconchoidal, breaking through the grains.

Cleavage

None (quartz itself has no cleavage, and the interlocking texture prevents rock cleavage).

Composition

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

Physical characteristics

• Crystal Habit: Anhedral, interlocking granular mosaic.
• Cleavage Type: Absent.
• Fracture Type: Conchoidal to subconchoidal.
• Tenacity: Brittle, extremely tough and durable.
• Luster Type: Vitreous to greasy.

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