How to identify Quartz in Metamorphic Rock

To correctly identify Quartz in Metamorphic Rock (Quartz (SiO2) in Metamorphic Rock (likely schist or gneiss)), 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 colorless, white, or gray within the metamorphic matrix. Can be stained by other minerals.

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

   In schist, quartz grains are often elongated and intergrown with micas, contributing to a foliated texture. In gneiss, quartz forms granular layers or lenses, contributing to the banded texture. Grains are typically anhedral to subhedral, with interlocking boundaries due to recrystallization.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Anhedral to subhedral grains, often flattened or elongated parallel to foliation in schist, or forming granular aggregates in gneiss. Well-formed euhedral crystals are rare in metamorphic rocks unless found in veins or vugs.

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

   Regional metamorphic terrains, contact metamorphic aureoles, and shear zones. Common in mountain belts and ancient cratons where continental crust has undergone significant deformation and metamorphism.

Key Facts

Hardness

7 (Mohs scale)

Specific Gravity

2.65 g/cm³

Crystal System

Trigonal (alpha-quartz, stable at surface conditions)

Color

Colorless, white, gray, but can be various colors due to impurities (e.g., rose quartz, amethyst). In metamorphic rocks, often appears colorless to gray.

Luster

Vitreous to greasy

Transparency

Transparent to translucent

Fracture

Conchoidal

Cleavage

None

Composition

Silicon dioxide (SiO2)

Physical characteristics

• Crystal Habit: Anhedral to subhedral grains, often elongated or flattened in metamorphic rocks due to recrystallization and deformation. Can form granular aggregates.
• Cleavage Type: Absent
• Fracture Type: Conchoidal
• Tenacity: Brittle
• Luster Type: Vitreous (glassy) to greasy

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