How to identify Quartz Vein in Metamorphic Rock

To correctly identify Quartz Vein in Metamorphic Rock (Quartz (SiO2) in a host rock, likely a schist or gneiss due to the dark, foliated appearance and presence of iron staining), 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

   Quartz: Typically milky white, translucent to transparent, sometimes gray or smoky. Host rock: Dark gray, black, greenish-black, or brownish, depending on mineralogy. Iron staining: Reddish-brown, yellowish-orange.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Quartz: Vitreous (glassy). Host rock: Dull to sub-vitreous, sometimes silky on foliation planes (schist).

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Quartz: Granular, massive, sometimes crystalline with euhedral faces in vugs. Host rock: Foliated (schistose or gneissic), fine- to medium-grained.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz: Anhedral to subhedral grains within the vein, sometimes euhedral hexagonal prisms with pyramidal terminations in open spaces (vugs).

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz: None (conchoidal fracture). Host rock: Exhibits schistosity or gneissic banding, which is a planar fabric, not true mineral cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Common in regions that have undergone regional metamorphism, particularly in mountain belts, cratonic shields, and areas with significant hydrothermal alteration. Often associated with fault zones, shear zones, and areas of intense deformation.

Key Facts

Hardness

Quartz: 7 on Mohs scale. Host rock: Variable, typically 3-6 depending on mineralogy.

Specific Gravity

Quartz: 2.65 g/cm³. Host rock: 2.7-3.0 g/cm³.

Crystal System

Quartz: Trigonal. Host rock: Monoclinic, orthorhombic, etc., depending on constituent minerals.

Color

Quartz: Colorless, white, gray, smoky. Host rock: Dark gray, black, green, brown. Iron staining: Reddish-brown, yellow.

Luster

Quartz: Vitreous. Host rock: Dull, sub-vitreous, silky.

Transparency

Quartz: Transparent to translucent. Host rock: Opaque.

Fracture

Quartz: Conchoidal. Host rock: Irregular, splintery.

Cleavage

Quartz: None. Host rock: Foliation (schistosity/gneissic banding) is a planar fabric, not true cleavage.

Composition

Quartz: Silicon dioxide (SiO2). Host rock: Silicates (e.g., micas, feldspars, amphiboles, garnets, quartz).

Physical characteristics

• Crystal Habit: Quartz: Massive, granular, sometimes prismatic in vugs. Host rock: Platy (micas), prismatic (amphiboles), granular (feldspars, quartz).
• Cleavage Type: Quartz: Absent. Host rock: Perfect in micas (basal), good in amphiboles (prismatic), poor to absent in quartz/feldspar.
• Fracture Type: Quartz: Conchoidal. Host rock: Irregular, splintery, hackly.
• Tenacity: Quartz: Brittle. Host rock: Brittle.
• Luster Type: Quartz: Vitreous. Host rock: Dull, sub-vitreous, silky (on foliation planes).

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