How to identify Quartzite

To correctly identify Quartzite (Metamorphic rock, predominantly 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

   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 on freshly broken surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Granoblastic (non-foliated, interlocking granular texture). The original sand grains are no longer visible as distinct clasts; instead, they have recrystallized into a mosaic of intergrown quartz crystals. The rock breaks across grain boundaries, not around them.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Individual quartz crystals are anhedral (lacking well-formed crystal faces) due to mutual interference during recrystallization, forming an interlocking mosaic.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   No true cleavage due to the interlocking nature of the quartz grains. It exhibits conchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in regions that have undergone significant regional metamorphism, such as ancient mountain belts (orogenic zones), cratonic shields, and deeply buried sedimentary basins. It is often associated with other metamorphic rocks like schists and gneisses, and sometimes with igneous intrusions that provided the heat for metamorphism.

Key Facts

Hardness

7 on the Mohs scale

Specific Gravity

2.65 g/cm (same as quartz)

Crystal System

Trigonal (for the constituent quartz crystals)

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 across grain boundaries.

Cleavage

None (though individual quartz crystals may show poor rhombohedral cleavage, it is not observed in the rock mass).

Composition

Predominantly quartz (SiO), typically >90-95%. Minor accessory minerals may include mica, feldspar, garnet, magnetite, rutile, zircon, and tourmaline.

Physical characteristics

• Crystal Habit: Granoblastic, interlocking mosaic of anhedral quartz grains.
• Cleavage Type: Absent in the rock mass; individual quartz crystals have poor rhombohedral cleavage.
• Fracture Type: Conchoidal to subconchoidal.
• Tenacity: Brittle.
• Luster Type: Vitreous to greasy.

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