How to identify Pyrite in Quartz Vein

To correctly identify Pyrite in Quartz Vein (FeS2 (Pyrite) in SiO2 (Quartz)), 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

   Pyrite: Brassy yellow, pale brass-yellow, or gold-like. Quartz: Colorless, white, grey, or smoky.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Pyrite: Metallic, splendent. Quartz: Vitreous (glassy) to greasy.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Pyrite: Crystalline, granular, massive. Quartz: Crystalline, massive, granular. The overall texture of the vein can be massive, banded, or vuggy.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Pyrite: Commonly forms cubes, pyritohedrons (12 pentagonal faces), octahedrons, or combinations thereof. Striations are often visible on cube faces. Quartz: Can be anhedral (massive, irregular grains) or euhedral (hexagonal prisms terminated by rhombohedra).

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Pyrite: Indistinct to poor cleavage on {001}. Quartz: No cleavage, conchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Typically found in hydrothermal veins associated with igneous intrusions, metamorphic terrains, and sedimentary rocks that have undergone hydrothermal alteration. Common in mesothermal and epithermal gold deposits, porphyry copper deposits, and volcanogenic massive sulfide (VMS) deposits.

Key Facts

Hardness

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

Specific Gravity

Pyrite: 4.95-5.03; Quartz: 2.65.

Crystal System

Pyrite: Isometric; Quartz: Trigonal.

Color

Pyrite: Pale brass-yellow, gold-like; Quartz: Colorless, white, grey, smoky.

Luster

Pyrite: Metallic; Quartz: Vitreous to greasy.

Transparency

Pyrite: Opaque; Quartz: Transparent to translucent.

Fracture

Pyrite: Uneven to conchoidal; Quartz: Conchoidal.

Cleavage

Pyrite: Indistinct to poor on {001}; Quartz: None.

Composition

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

Physical characteristics

• Crystal Habit: Pyrite: Cubes, pyritohedrons, octahedrons, massive, granular, radiating. Quartz: Prismatic, massive, granular, cryptocrystalline.
• Cleavage Type: Pyrite: Poor/Indistinct; Quartz: None.
• Fracture Type: Pyrite: Uneven to conchoidal; Quartz: Conchoidal.
• Tenacity: Pyrite: Brittle; Quartz: Brittle.
• Luster Type: Pyrite: Metallic; Quartz: Vitreous to greasy.

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