How to identify Quartz with Pyrite

To correctly identify Quartz with Pyrite (Quartz (SiO2) and Pyrite (FeS2)), 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 can be colorless, white, milky, smoky, purple (amethyst), yellow (citrine), or pink (rose quartz). Pyrite is brassy yellow to golden, often with a tarnished iridescent sheen.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Quartz typically has a vitreous (glassy) luster. Pyrite has a distinct metallic luster.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Quartz can be crystalline, massive, or granular. Pyrite crystals are often cubic, octahedral, or pyritohedral, and can be disseminated or form aggregates within the quartz matrix.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz commonly forms hexagonal prisms terminated by hexagonal pyramids. Pyrite forms distinct cubic, octahedral, or pyritohedral crystals, often with striations on cube faces.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz has no true cleavage, exhibiting conchoidal fracture. Pyrite has very poor cleavage on {001} and {110}, but typically fractures conchoidally or unevenly.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal veins, metamorphic rocks (e.g., schists, gneisses), sedimentary rocks (e.g., black shales, coal seams), and volcanogenic massive sulfide (VMS) deposits.

Key Facts

Hardness

Quartz: 7 on Mohs scale; Pyrite: 6-6.5 on Mohs scale.

Specific Gravity

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

Crystal System

Quartz: Trigonal; Pyrite: Isometric (Cubic).

Color

Quartz: Colorless, white, milky, smoky, purple, yellow, pink; Pyrite: Brassy yellow, golden.

Luster

Quartz: Vitreous; Pyrite: Metallic.

Transparency

Quartz: Transparent to opaque; Pyrite: Opaque.

Fracture

Quartz: Conchoidal; Pyrite: Conchoidal to uneven.

Cleavage

Quartz: None; Pyrite: Very poor on {001} and {110}.

Composition

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

Physical characteristics

• Crystal Habit: Quartz: Prismatic, massive, granular; Pyrite: Cubic, octahedral, pyritohedral, massive, reniform, radiating.
• Cleavage Type: Quartz: Absent; Pyrite: Very poor.
• Fracture Type: Quartz: Conchoidal; Pyrite: Conchoidal to uneven.
• Tenacity: Quartz: Brittle; Pyrite: Brittle.
• Luster Type: Quartz: Vitreous; Pyrite: Metallic.

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