How to identify Weathered Metamorphic Rock with Quartz Veins

To correctly identify Weathered Metamorphic Rock with Quartz Veins (Metamorphic rock (likely schist or gneiss) with quartz (SiO2) veins), 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

   Variable for the host metamorphic rock (e.g., grey, black, green, brown, reddish-brown due to iron oxidation from weathering). Quartz veins are typically white, milky, or translucent. Weathering often imparts duller, earthy tones to the host rock.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Host rock: Dull to earthy on weathered surfaces; fresh surfaces may show pearly (micas in schist) or vitreous (feldspar, quartz in gneiss) luster. Quartz veins: Vitreous to greasy.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Host rock: Foliated (schistose or gneissic) with visible mineral alignment. Weathered surfaces may be rough, pitted, or friable. Quartz veins: Granular, massive, or crystalline, often cutting across the foliation of the host rock.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Host rock: Platy minerals (micas) in schist, granular interlocking crystals (quartz, feldspar) in gneiss. Quartz veins: Anhedral to subhedral quartz crystals, often massive or forming interlocking grains within the vein.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Host rock: Schist may exhibit excellent cleavage (schistosity) due to parallel alignment of micas. Gneiss has poor to no cleavage but exhibits gneissic banding. Quartz veins: No true cleavage, but conchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Common in ancient mountain belts, cratonic shields, and areas that have undergone regional metamorphism. Often found in outcrops, road cuts, and stream beds where erosion has exposed the bedrock. Weathering is most pronounced in humid and temperate climates.

Key Facts

Hardness

Host rock: Variable (e.g., micas 2-3, feldspar 6, quartz 7). Quartz veins: 7 (Mohs scale).

Specific Gravity

Host rock: 2.6-3.0 g/cm³ (variable depending on mineralogy). Quartz veins: 2.65 g/cm³.

Crystal System

Host rock: Polycrystalline, individual minerals may be monoclinic, triclinic, or orthorhombic. Quartz veins: Trigonal (for quartz).

Color

Host rock: Grey, black, green, brown, reddish-brown (weathered). Quartz veins: White, milky, translucent.

Luster

Host rock: Dull, earthy (weathered); fresh surfaces may be pearly or vitreous. Quartz veins: Vitreous to greasy.

Transparency

Host rock: Opaque to translucent. Quartz veins: Translucent to transparent.

Fracture

Host rock: Irregular, splintery. Quartz veins: Conchoidal.

Cleavage

Host rock: Schistosity (perfect in one direction for micas), gneissic banding (no true cleavage). Quartz veins: None.

Composition

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

Physical characteristics

• Crystal Habit: Host rock: Foliated (schistose or gneissic), granular. Quartz veins: Massive, anhedral to subhedral crystals.
• Cleavage Type: Host rock: Perfect basal (micas in schist), none (quartz, feldspar). Quartz veins: None.
• Fracture Type: Host rock: Irregular, splintery. Quartz veins: Conchoidal.
• Tenacity: Host rock: Brittle to friable (weathered). Quartz veins: Brittle.
• Luster Type: Host rock: Dull, earthy (weathered); fresh surfaces may be pearly, vitreous. Quartz veins: Vitreous, greasy.

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