How to identify Quartz with Sulfide Mineralization

To correctly identify Quartz with Sulfide Mineralization (SiO2 with associated sulfide minerals (e.g., pyrite, chalcopyrite)), 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 is typically colorless, white, or grey, but can be stained by associated sulfides (e.g., reddish-brown from iron oxides after pyrite, green from copper minerals). Sulfides exhibit characteristic colors: pyrite (brassy yellow), chalcopyrite (brassy yellow, often tarnished iridescent), galena (lead-grey), sphalerite (yellow, brown, black), arsenopyrite (silver-white to steel-grey).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Quartz has a vitreous (glassy) luster. Sulfide minerals typically have a metallic luster, though some can be submetallic or resinous (e.g., sphalerite).

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Can range from massive, granular, or crystalline quartz with disseminated sulfides, to banded or veined textures where sulfides form distinct layers or infillings within quartz. Sulfide crystals can be euhedral (well-formed), subhedral, or anhedral.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz often forms hexagonal prisms with pyramidal terminations, or can be anhedral in massive aggregates. Sulfides exhibit various crystal forms: pyrite (cubes, octahedra, pyritohedra), galena (cubes, octahedra), chalcopyrite (tetrahedral, often massive), sphalerite (tetrahedral, dodecahedral, often massive).

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz lacks cleavage, exhibiting conchoidal fracture. Sulfide minerals vary: galena (perfect cubic cleavage), sphalerite (perfect dodecahedral cleavage), pyrite and chalcopyrite (poor or no cleavage, irregular fracture).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal veins, stockworks, breccias, porphyry deposits, volcanogenic massive sulfide (VMS) deposits, epithermal deposits, mesothermal gold deposits, and skarn deposits. Often found in association with igneous intrusions or metamorphic terrains.

Key Facts

Hardness

Quartz: 7 (Mohs). Sulfides vary: pyrite (6-6.5), chalcopyrite (3.5-4), galena (2.5), sphalerite (3.5-4).

Specific Gravity

Quartz: 2.65. Sulfides are significantly denser: pyrite (4.95-5.10), chalcopyrite (4.1-4.3), galena (7.4-7.6), sphalerite (3.9-4.1). The aggregate density will be higher than pure quartz.

Crystal System

Quartz: Trigonal. Sulfides vary: pyrite (Isometric), chalcopyrite (Tetragonal), galena (Isometric), sphalerite (Isometric).

Color

See 'color' in 'howToIdentify'.

Luster

See 'luster' in 'howToIdentify'.

Transparency

Quartz: Transparent to translucent. Sulfides: Opaque.

Fracture

Quartz: Conchoidal. Sulfides: Irregular to subconchoidal.

Cleavage

Quartz: None. Sulfides: Variable (e.g., galena perfect cubic, sphalerite perfect dodecahedral, pyrite/chalcopyrite poor/none).

Composition

SiO2 (quartz) + various metal sulfides (e.g., FeS2, CuFeS2, PbS, ZnS).

Physical characteristics

• Crystal Habit: Quartz: Prismatic, massive, granular. Sulfides: Cubic, octahedral, tetrahedral, massive, disseminated.
• Cleavage Type: Quartz: Absent. Sulfides: Variable (e.g., perfect cubic for galena, perfect dodecahedral for sphalerite).
• Fracture Type: Quartz: Conchoidal. Sulfides: Irregular to subconchoidal.
• Tenacity: Quartz: Brittle. Sulfides: Brittle (most), sectile (some, e.g., galena).
• Luster Type: Vitreous (quartz) and Metallic (sulfides).

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