How to identify Sphalerite

To correctly identify Sphalerite (Sphalerite (ZnS)), 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

   Highly variable: commonly yellow, brown, black, red, green, or colorless. Darker colors are due to increasing iron content. Transparent to translucent varieties are less common.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Resinous to adamantine, sometimes submetallic in very dark, iron-rich varieties (marmatite).

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Often crystalline, granular, massive, or botryoidal. Crystals are typically tetrahedral or dodecahedral.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Isometric system, typically forming tetrahedral, dodecahedral, or less commonly cubic crystals. Often twinned, particularly penetration twins. Can also be massive, granular, or stalactitic.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Perfect dodecahedral cleavage in six directions, producing rhombic dodecahedral fragments. This is a key diagnostic feature.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal veins, volcanogenic massive sulfide (VMS) deposits, Mississippi Valley-type (MVT) deposits, contact metamorphic deposits, and less commonly in sedimentary rocks. Associated minerals often include galena, pyrite, chalcopyrite, quartz, calcite, dolomite, and fluorite.

Key Facts

Hardness

3.5-4 on the Mohs scale

Specific Gravity

3.9-4.1 (increases with iron content)

Crystal System

Isometric

Color

Highly variable (yellow, brown, black, red, green, colorless)

Luster

Resinous to adamantine

Transparency

Transparent to opaque

Fracture

Conchoidal to uneven

Cleavage

Perfect dodecahedral in six directions

Composition

Zinc sulfide (ZnS), often with significant iron (Fe) substitution, and minor amounts of cadmium (Cd), manganese (Mn), gallium (Ga), indium (In), and germanium (Ge).

Physical characteristics

• Crystal Habit: Tetrahedral, dodecahedral, cubic, massive, granular, botryoidal, stalactitic
• Cleavage Type: Perfect dodecahedral {011}
• Fracture Type: Conchoidal to uneven
• Tenacity: Brittle
• Luster Type: Resinous to adamantine, sometimes submetallic

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