How to identify Chalcopyrite in Quartz

To correctly identify Chalcopyrite in Quartz (CuFeS2 in SiO2), 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

   Chalcopyrite: Brassy yellow, often tarnishing to iridescent blues, purples, and reds. Quartz: Colorless, white, gray, or smoky. The contrast between the metallic chalcopyrite and the vitreous quartz is distinctive.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Chalcopyrite: Metallic. Quartz: Vitreous to greasy.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Chalcopyrite: Typically massive, granular, or as disseminated crystals within the quartz. Quartz: Crystalline, massive, or granular.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Chalcopyrite: Tetragonal, often forming pseudotetrahedral crystals, but more commonly massive. Quartz: Hexagonal, often forming prismatic crystals with pyramidal terminations, or massive.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Chalcopyrite: Poor, indistinct. Quartz: None (conchoidal fracture).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal veins, porphyry copper deposits, volcanogenic massive sulfide (VMS) deposits, contact metamorphic deposits, and sedimentary exhalative (SEDEX) deposits.

Key Facts

Hardness

Chalcopyrite: 3.5-4 (Mohs); Quartz: 7 (Mohs)

Specific Gravity

Chalcopyrite: 4.1-4.3; Quartz: 2.65

Crystal System

Chalcopyrite: Tetragonal; Quartz: Trigonal (often referred to as hexagonal)

Color

Chalcopyrite: Brassy yellow, often tarnished iridescent; Quartz: Colorless, white, gray, smoky

Luster

Chalcopyrite: Metallic; Quartz: Vitreous to greasy

Transparency

Chalcopyrite: Opaque; Quartz: Transparent to translucent

Fracture

Chalcopyrite: Uneven to conchoidal; Quartz: Conchoidal

Cleavage

Chalcopyrite: Poor, indistinct {011}; Quartz: None

Composition

Chalcopyrite: Copper iron sulfide (CuFeS2); Quartz: Silicon dioxide (SiO2)

Physical characteristics

• Crystal Habit: Chalcopyrite: Massive, disseminated grains, rarely distinct pseudotetrahedral crystals. Quartz: Massive, granular, prismatic crystals.
• Cleavage Type: Chalcopyrite: Poor, indistinct. Quartz: Absent.
• Fracture Type: Chalcopyrite: Uneven to conchoidal. Quartz: Conchoidal.
• Tenacity: Chalcopyrite: Brittle. Quartz: Brittle.
• Luster Type: Chalcopyrite: Metallic. Quartz: Vitreous to greasy.

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