How to identify Quartz with Sulfide Mineralization

To correctly identify Quartz with Sulfide Mineralization (SiO2 with associated sulfide minerals), 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 white, milky, gray, or colorless. Sulfide minerals introduce metallic colors: brassy yellow (pyrite), golden yellow (chalcopyrite), silvery gray (galena), dark brown to black (sphalerite), or reddish-brown (pyrrhotite). Oxidation of sulfides can lead to reddish-brown (iron oxides), green (copper carbonates), or blue (copper sulfates) staining.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Quartz exhibits a vitreous (glassy) luster. Sulfide minerals have a distinct metallic luster, which can be bright, dull, or tarnished.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Can range from massive, fine-grained quartz with disseminated sulfides to coarse-grained quartz crystals intergrown with euhedral to anhedral sulfide crystals. Sulfides may form distinct bands, blebs, or fracture fillings within the quartz.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz often forms hexagonal prisms with pyramidal terminations, or anhedral masses. Sulfides can occur as euhedral crystals (e.g., cubic pyrite, octahedral galena), anhedral grains, or massive aggregates.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz has no cleavage, exhibiting conchoidal fracture. Sulfide minerals vary: galena has perfect cubic cleavage, sphalerite has perfect dodecahedral cleavage, pyrite has no cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Typically found in hydrothermal vein systems, stockworks, breccia pipes, and replacement deposits associated with igneous intrusions, fault zones, and metamorphic terrains. Common in orogenic gold deposits, porphyry copper deposits, epithermal deposits, and VMS deposits.

Key Facts

Hardness

Quartz: 7 on Mohs scale. Sulfides vary: Pyrite (6-6.5), Chalcopyrite (3.5-4), Galena (2.5), Sphalerite (3.5-4).

Specific Gravity

Quartz: 2.65 g/cm³. Sulfides are denser: Pyrite (4.95-5.10), Chalcopyrite (4.1-4.3), Galena (7.4-7.6), Sphalerite (3.9-4.1). The overall specific gravity of the rock will be higher than pure quartz, proportional to the sulfide content.

Crystal System

Quartz: Trigonal. Sulfides vary: Pyrite (Isometric), Chalcopyrite (Tetragonal), Galena (Isometric), Sphalerite (Isometric).

Color

Quartz: Colorless, white, gray, milky. Sulfides: Brassy yellow, golden yellow, silvery gray, dark brown, black, etc.

Luster

Vitreous (quartz) to metallic (sulfides).

Transparency

Quartz: Transparent to translucent to opaque. Sulfides: Opaque.

Fracture

Quartz: Conchoidal. Sulfides vary: Pyrite (uneven to conchoidal), Chalcopyrite (uneven), Galena (subconchoidal), Sphalerite (conchoidal).

Cleavage

Quartz: None. Sulfides vary: Galena (perfect cubic), Sphalerite (perfect dodecahedral), Pyrite (none).

Composition

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

Physical characteristics

• Crystal Habit: Quartz: Prismatic, massive, granular. Sulfides: Cubic, octahedral, tetrahedral, massive, granular, disseminated.
• Cleavage Type: Quartz: Absent. Sulfides: Variable (e.g., perfect cubic for galena, perfect dodecahedral for sphalerite).
• Fracture Type: Quartz: Conchoidal. Sulfides: Uneven, subconchoidal, or conchoidal.
• Tenacity: Quartz: Brittle. Sulfides: Brittle.
• Luster Type: Vitreous (quartz) to metallic (sulfides).

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