How to identify Quartz with Sphalerite

To correctly identify Quartz with Sphalerite (SiO2 (Quartz) with (Zn,Fe)S (Sphalerite)), 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: Colorless, white, gray, purple (amethyst), yellow (citrine), pink (rose quartz), brown (smoky quartz). Sphalerite: Typically yellow, brown, red, black; often resinous to submetallic luster. Streak is yellowish-brown to brown.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Quartz: Vitreous. Sphalerite: Resinous to adamantine, sometimes submetallic.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Quartz: Crystalline, granular, massive. Sphalerite: Crystalline, granular, massive.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz: Hexagonal prisms with pyramidal terminations, massive, granular. Sphalerite: Tetrahedral, dodecahedral, or complex isometric crystals; often massive, granular, or botryoidal.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz: None (conchoidal fracture). Sphalerite: Perfect dodecahedral cleavage in 6 directions.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal veins, skarns, volcanogenic massive sulfide (VMS) deposits, Mississippi Valley-type (MVT) deposits.

Key Facts

Hardness

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

Specific Gravity

Quartz: 2.65; Sphalerite: 3.9-4.1 (increases with Fe content)

Crystal System

Quartz: Trigonal; Sphalerite: Isometric

Color

Quartz: Colorless, white, various; Sphalerite: Yellow, brown, red, black.

Luster

Quartz: Vitreous; Sphalerite: Resinous to adamantine.

Transparency

Quartz: Transparent to translucent; Sphalerite: Translucent to opaque.

Fracture

Quartz: Conchoidal; Sphalerite: Uneven to conchoidal.

Cleavage

Quartz: None; Sphalerite: Perfect dodecahedral in 6 directions.

Composition

Quartz: Silicon dioxide (SiO2); Sphalerite: Zinc iron sulfide ((Zn,Fe)S).

Physical characteristics

• Crystal Habit: Quartz: Prismatic, massive, granular; Sphalerite: Tetrahedral, dodecahedral, massive, granular, botryoidal.
• Cleavage Type: Quartz: Absent; Sphalerite: Perfect dodecahedral.
• Fracture Type: Quartz: Conchoidal; Sphalerite: Uneven to conchoidal.
• Tenacity: Quartz: Brittle; Sphalerite: Brittle.
• Luster Type: Quartz: Vitreous; Sphalerite: Resinous to adamantine.

Explore Quartz with Sphalerite