How to identify Quartz with Sulfide Mineral

To correctly identify Quartz with Sulfide Mineral (SiO2 with sulfide inclusion), 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 can be colorless, white, gray, smoky, purple (amethyst), or yellow (citrine). Sulfide inclusions will appear as distinct metallic colors: brassy yellow (pyrite, chalcopyrite), silvery gray (galena, arsenopyrite), dark gray to black (sphalerite, pyrrhotite), or iridescent tarnish. The overall color of the specimen will be a combination of the quartz and the sulfides.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Quartz exhibits a vitreous (glassy) luster. Sulfide inclusions will display a distinct metallic luster, often bright and reflective.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   The texture can range from massive to crystalline. Quartz may form euhedral crystals, anhedral grains, or cryptocrystalline masses. Sulfides can be disseminated as fine grains, form distinct euhedral to subhedral crystals, or occur as irregular masses and veinlets within the quartz.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz typically forms hexagonal prisms terminated by rhombohedra. Sulfides can exhibit various crystal forms depending on the species (e.g., cubes or pyritohedrons for pyrite, tetrahedra for sphalerite, cubes for galena), or they may be anhedral.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz has no true cleavage, exhibiting conchoidal fracture. Sulfide minerals often have distinct cleavage: pyrite (poor to indistinct), chalcopyrite (poor), galena (perfect cubic), sphalerite (perfect dodecahedral), arsenopyrite (distinct prismatic).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal veins, porphyry deposits, skarns, epithermal deposits, mesothermal deposits, and other ore-forming systems associated with magmatic or metamorphic processes. Often found in fault zones, shear zones, and intrusive contacts.

Key Facts

Hardness

Quartz: 7 on Mohs scale. Sulfides: Pyrite (6-6.5), Chalcopyrite (3.5-4), Galena (2.5), Sphalerite (3.5-4), Arsenopyrite (5.5-6). The overall hardness will be dominated by quartz but can be scratched in areas with softer sulfides.

Specific Gravity

Quartz: 2.65 g/cm³. Sulfides: Pyrite (4.95-5.10), Chalcopyrite (4.1-4.3), Galena (7.4-7.6), Sphalerite (3.9-4.1), Arsenopyrite (5.9-6.2). Specimens with significant sulfide content will have a higher specific gravity than pure quartz.

Crystal System

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

Color

Variable for quartz; metallic colors for sulfides (brassy yellow, silvery gray, dark gray/black).

Luster

Vitreous for quartz; metallic for sulfides.

Transparency

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

Fracture

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

Cleavage

Quartz: None. Sulfides: Pyrite (poor/indistinct), Chalcopyrite (poor), Galena (perfect cubic), Sphalerite (perfect dodecahedral), Arsenopyrite (distinct prismatic).

Composition

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

Physical characteristics

• Crystal Habit: Quartz: Prismatic, massive, granular. Sulfides: Euhedral crystals (cubes, pyritohedrons, tetrahedra), massive, granular, disseminated.
• Cleavage Type: Quartz: Absent. Sulfides: Variable, from perfect (galena, sphalerite) to poor/indistinct (pyrite, chalcopyrite).
• Fracture Type: Quartz: Conchoidal. Sulfides: Uneven to conchoidal.
• Tenacity: Quartz: Brittle. Sulfides: Brittle (most sulfides).
• Luster Type: Quartz: Vitreous. Sulfides: Metallic.

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