How to identify Quartz-Pyrite Vein

To correctly identify Quartz-Pyrite Vein (Quartz (SiO2) and Pyrite (FeS2) in a host rock (likely a sulfide-rich metamorphic or igneous rock)), 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 colorless, white, or milky white, but can be gray, yellow, or smoky. Pyrite: Brassy yellow, metallic. Host Rock: Varies widely depending on lithology, but often dark gray to black if carbonaceous, or greenish/reddish if altered igneous/metamorphic.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Quartz: Vitreous (glassy) to greasy. Pyrite: Metallic. Host Rock: Variable, can be dull, earthy, or vitreous depending on mineralogy.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Quartz: Granular, massive, or crystalline (euhedral to anhedral). Pyrite: Crystalline (often cubic or octahedral), massive, or disseminated. Host Rock: Fine-grained to coarse-grained, foliated (metamorphic) or equigranular (igneous).

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz: Hexagonal prisms with pyramidal terminations (if euhedral), massive, or anhedral grains. Pyrite: Cubes, octahedra, pyritohedra, or massive aggregates. Host Rock: Constituent minerals show their characteristic crystal forms.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz: None (conchoidal fracture). Pyrite: Indistinct to poor cubic cleavage (often appears as conchoidal fracture). Host Rock: Variable, depends on constituent minerals (e.g., mica in schist will have perfect cleavage).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal alteration zones, fault zones, shear zones, contact metamorphic aureoles, volcanic arcs, sedimentary basins with active hydrothermal systems.

Key Facts

Hardness

Quartz: 7 (Mohs). Pyrite: 6-6.5 (Mohs).

Specific Gravity

Quartz: 2.65 g/cm³. Pyrite: 4.95-5.10 g/cm³.

Crystal System

Quartz: Trigonal. Pyrite: Isometric.

Color

Quartz: Colorless, white, milky, smoky, yellow. Pyrite: Brassy yellow.

Luster

Quartz: Vitreous to greasy. Pyrite: Metallic.

Transparency

Quartz: Transparent to translucent to opaque. Pyrite: Opaque.

Fracture

Quartz: Conchoidal. Pyrite: Uneven to conchoidal.

Cleavage

Quartz: None. Pyrite: Indistinct to poor {100}.

Composition

Quartz: Silicon dioxide (SiO2). Pyrite: Iron disulfide (FeS2).

Physical characteristics

• Crystal Habit: Quartz: Prismatic, massive, granular. Pyrite: Cubic, octahedral, pyritohedral, massive, granular.
• Cleavage Type: Quartz: Absent. Pyrite: Poor/indistinct cubic.
• Fracture Type: Quartz: Conchoidal. Pyrite: Uneven to conchoidal.
• Tenacity: Quartz: Brittle. Pyrite: Brittle.
• Luster Type: Quartz: Vitreous to greasy. Pyrite: Metallic.

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