How to identify Quartzite with Pyrite

To correctly identify Quartzite with Pyrite (Quartzite (metamorphic rock) with 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

   Quartzite: Typically white, gray, pink, reddish, or purplish. Pyrite: Brassy yellow, metallic. The overall rock color will be a combination.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Quartzite: Vitreous (glassy) to greasy. Pyrite: Metallic.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Granoblastic, interlocking quartz grains, often sugary. Pyrite appears as distinct metallic grains within this matrix.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartzite: Anhedral to subhedral interlocking quartz grains. Pyrite: Commonly euhedral cubes, pyritohedrons, or octahedrons, but can also be anhedral masses or disseminated grains.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartzite: No true cleavage, conchoidal to splintery fracture. Pyrite: Indistinct cleavage on {001} and {111}, but typically fractures conchoidally.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Formed from the metamorphism of quartz-rich sandstones in regional metamorphic belts (e.g., mountain ranges) or contact metamorphic aureoles. Pyrite's presence suggests reducing conditions during either sedimentation or metamorphism, often associated with organic matter or hydrothermal activity.

Key Facts

Hardness

Quartz (7 on Mohs scale), Pyrite (6-6.5 on Mohs scale). The overall rock is very hard.

Specific Gravity

Quartzite (2.65 g/cm³), Pyrite (4.95-5.10 g/cm³). The rock's specific gravity will be slightly higher than pure quartzite depending on pyrite content.

Crystal System

Quartz (Trigonal), Pyrite (Isometric).

Color

Quartzite: Variable (white, gray, pink, red). Pyrite: Brassy yellow.

Luster

Quartzite: Vitreous to greasy. Pyrite: Metallic.

Transparency

Quartzite: Translucent to opaque. Pyrite: Opaque.

Fracture

Quartzite: Conchoidal to splintery. Pyrite: Uneven to conchoidal.

Cleavage

Quartzite: None. Pyrite: Poor/indistinct on {001} and {111}.

Composition

Predominantly SiO2 (quartz) with FeS2 (pyrite) as an accessory mineral.

Physical characteristics

• Crystal Habit: Quartz: Granular, interlocking anhedral to subhedral grains. Pyrite: Euhedral cubes, pyritohedrons, octahedrons, or massive/disseminated.
• Cleavage Type: Quartz: None. Pyrite: Poor/indistinct.
• Fracture Type: Quartz: Conchoidal to splintery. Pyrite: Uneven to conchoidal.
• Tenacity: Quartz: Brittle. Pyrite: Brittle.
• Luster Type: Quartz: Vitreous to greasy. Pyrite: Metallic.

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