How to identify Quartz with Pyrite

To correctly identify Quartz with Pyrite (SiO2 (Quartz) with FeS2 (Pyrite) in a metamorphic or igneous host 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; can be gray, purple (amethyst), pink (rose quartz), yellow (citrine), or brown (smoky quartz) depending on impurities. Pyrite: Pale brass-yellow, metallic. Host Rock: Variable, depending on its type (e.g., gray for granite, dark green for schist, banded for gneiss).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Quartz: Vitreous (glassy). Pyrite: Metallic, splendent. Host Rock: Variable, often dull to vitreous.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Quartz: Crystalline, granular, massive, or drusy. Pyrite: Crystalline (often euhedral cubes, octahedra, pyritohedra), granular, massive. Host Rock: Variable, e.g., phaneritic (coarse-grained) for granite, foliated for schist/gneiss, aphanitic (fine-grained) for volcanic rocks.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz: Hexagonal prisms with pyramidal terminations (when euhedral), massive, granular. Pyrite: Cubes, octahedra, pyritohedra, often striated faces, massive. Host Rock: Constituent minerals show their characteristic crystal forms or textures.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz: None (conchoidal fracture). Pyrite: Indistinct to poor on {001}. Host Rock: Variable, depends on constituent minerals (e.g., mica in schist has perfect cleavage).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal veins, disseminated in altered igneous and metamorphic rocks, contact metamorphic zones, volcanogenic massive sulfide (VMS) deposits, porphyry copper deposits, orogenic gold deposits.

Key Facts

Hardness

Quartz: 7 on Mohs scale. Pyrite: 6-6.5 on Mohs scale. Host Rock: Variable, depending on its constituent minerals.

Specific Gravity

Quartz: 2.65 g/cm³. Pyrite: 4.95-5.10 g/cm³. Host Rock: Variable, typically 2.6-3.0 g/cm³.

Crystal System

Quartz: Trigonal. Pyrite: Isometric. Host Rock: Constituent minerals have their own crystal systems.

Color

Quartz: Colorless, white, various. Pyrite: Pale brass-yellow. Host Rock: Variable.

Luster

Quartz: Vitreous. Pyrite: Metallic. Host Rock: Variable.

Transparency

Quartz: Transparent to translucent. Pyrite: Opaque. Host Rock: Opaque.

Fracture

Quartz: Conchoidal. Pyrite: Uneven to conchoidal. Host Rock: Variable.

Cleavage

Quartz: None. Pyrite: Indistinct to poor. Host Rock: Variable.

Composition

Quartz: Silicon dioxide (SiO2). Pyrite: Iron disulfide (FeS2). Host Rock: Variable, e.g., granite (quartz, feldspar, mica), schist (mica, quartz, garnet), gneiss (feldspar, quartz, mica).

Physical characteristics

• Crystal Habit: Quartz: Prismatic, massive, granular. Pyrite: Cubic, octahedral, pyritohedral, massive, granular. Host Rock: Granular, foliated, massive.
• Cleavage Type: Quartz: None. Pyrite: Indistinct. Host Rock: Variable.
• Fracture Type: Quartz: Conchoidal. Pyrite: Uneven to conchoidal. Host Rock: Variable.
• Tenacity: Quartz: Brittle. Pyrite: Brittle. Host Rock: Variable.
• Luster Type: Quartz: Vitreous. Pyrite: Metallic. Host Rock: Variable.

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