How to identify Stibnite

To correctly identify Stibnite (Sb2S3), 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

   Lead-gray to silvery-white, often tarnishing to iridescent blue or black.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Bright metallic, sometimes dull on tarnished surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Often occurs in aggregates of acicular (needle-like), bladed, or columnar crystals. Can also be massive.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Orthorhombic system, typically forming elongated, prismatic crystals with striations parallel to the c-axis. Crystals can be bent or curved.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Perfect cleavage parallel to the length of the crystals ({010}), leading to easy breakage into splinters.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Low-temperature hydrothermal veins, hot spring deposits, and replacement deposits. Associated with quartz, calcite, barite, cinnabar, realgar, orpiment, and other sulfide minerals.

Key Facts

Hardness

2 on the Mohs scale (very soft, can be scratched by a fingernail)

Specific Gravity

4.52 - 4.62 (relatively heavy for a non-metallic mineral)

Crystal System

Orthorhombic

Color

Lead-gray to silvery-white, tarnishing to iridescent blue or black

Luster

Metallic

Transparency

Opaque

Fracture

Uneven to subconchoidal

Cleavage

Perfect on {010} (parallel to the length of the crystals)

Composition

Antimony sulfide (Sb2S3)

Physical characteristics

• Crystal Habit: Acicular, bladed, columnar, prismatic, massive, radiating aggregates. Crystals are often striated parallel to the c-axis and can be bent or curved.
• Cleavage Type: Perfect in one direction ({010}), leading to easy splitting into fibrous or splintery fragments.
• Fracture Type: Uneven to subconchoidal, but rarely observed due to perfect cleavage.
• Tenacity: Sectile (can be cut with a knife) and brittle.
• Luster Type: Metallic, sometimes dull on tarnished surfaces.

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