How to identify Quartz with Sulfides

To correctly identify Quartz with Sulfides (SiO2 with associated sulfide minerals (e.g., galena, sphalerite, or 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

   Variable. Quartz can be colorless, white, gray, or tinted. Sulfides exhibit characteristic colors: galena (silvery-gray), sphalerite (yellow, brown, black), chalcopyrite (brassy yellow), pyrite (pale brassy yellow), arsenopyrite (silvery-white).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Quartz typically has a vitreous (glassy) luster. Sulfide minerals generally exhibit a metallic luster.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Can be massive, crystalline, or banded. Quartz often forms euhedral to anhedral crystals within veins. Sulfides can be disseminated, massive, or form distinct crystals within the quartz matrix.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz often forms hexagonal prisms with pyramidal terminations. Sulfides can exhibit various crystal forms: galena (cubes, octahedra), sphalerite (tetrahedra, dodecahedra), chalcopyrite (tetrahedra, sphenoids), pyrite (cubes, pyritohedra).

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz has no cleavage (conchoidal fracture). Sulfides often have distinct cleavage: galena (perfect cubic), sphalerite (perfect dodecahedral), chalcopyrite (poor to indistinct).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal veins, stockworks, breccias, and disseminated occurrences within igneous, metamorphic, and sedimentary rocks, particularly in areas of past or present magmatic and tectonic activity.

Key Facts

Hardness

Quartz: 7 on Mohs scale. Sulfides vary: galena (2.5-2.75), sphalerite (3.5-4), chalcopyrite (3.5-4), pyrite (6-6.5).

Specific Gravity

Quartz: 2.65 g/cm³. Sulfides are denser: galena (7.4-7.6 g/cm³), sphalerite (3.9-4.1 g/cm³), chalcopyrite (4.1-4.3 g/cm³), pyrite (4.95-5.10 g/cm³).

Crystal System

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

Color

As described above, highly variable depending on the specific sulfide minerals present.

Luster

Vitreous for quartz, metallic for sulfides.

Transparency

Quartz can be transparent to opaque. Sulfides are opaque.

Fracture

Quartz: Conchoidal. Sulfides: often uneven or subconchoidal, but some show distinct cleavage.

Cleavage

Quartz: None. Sulfides: galena (perfect cubic), sphalerite (perfect dodecahedral), chalcopyrite (poor to indistinct).

Composition

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

Physical characteristics

• Crystal Habit: Quartz: Prismatic, massive, granular. Sulfides: Cubic, tetrahedral, massive, granular, disseminated.
• Cleavage Type: Quartz: Absent. Sulfides: Perfect cubic (galena), perfect dodecahedral (sphalerite), poor (chalcopyrite).
• Fracture Type: Quartz: Conchoidal. Sulfides: Uneven to subconchoidal.
• Tenacity: Quartz: Brittle. Sulfides: Brittle.
• Luster Type: Quartz: Vitreous. Sulfides: Metallic.

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