Rock Identifier

Stibnite Identification Guide

Identifying stibnite, the primary antimony ore, by its steel-gray bladed crystals, very low hardness, perfect cleavage, and high density.

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Stibnite Identification Guide

What Stibnite Looks Like

Stibnite is antimony sulfide (Sb2S3), the most important antimony ore. It is lead-gray to silvery steel-gray with a brilliant metallic luster on fresh surfaces, often tarnishing to a dull or iridescent blackish coating. Its hallmark is spectacular long, slender, prismatic to bladed crystals, frequently vertically striated and bent, curved, or twisted, that radiate or form sprays. It also occurs massive, granular, or columnar.

Step-by-Step Field ID

  1. Look for bladed crystals. Long, striated, blade- or needle-like steel-gray crystals, often bent, are nearly diagnostic.
  2. Test hardness. Very soft (Mohs 2); a fingernail barely fails but a copper coin and knife scratch it easily.
  3. Check cleavage. One perfect cleavage parallel to the length of the blades; crystals split into striated splinters.
  4. Streak it. Lead-gray to black streak.
  5. Heft it. Heavy (SG ~4.6).

Key Diagnostic Tests

  • Mohs hardness: 2, very soft.
  • Streak: lead-gray to black.
  • Cleavage: one perfect cleavage lengthwise; flexible, easily bent crystals.
  • Specific gravity: ~4.6.
  • Fusibility: melts in a candle flame (low melting point ~525 C), a classic confirming test; fuses easily and colors flame greenish.
  • Luster: bright metallic, splendent on fresh blades.

Common Look-Alikes

  • Galena: lead-gray and soft-ish but shows perfect CUBIC cleavage in three directions and is much denser (SG ~7.5); galena forms cubes, not bent blades.
  • Bismuthinite: very similar bladed habit and softness, but is heavier (SG ~6.8) and harder to fuse-distinguish; chemical/locality context helps.
  • Marcasite/arsenopyrite: much harder (Mohs 5.5-6) and brassy/silver-white, not soft gray blades.
  • Manganese oxides (e.g., pyrolusite): sooty, dull, and give a black streak but lack the bright bladed metallic crystals and easy fusibility.

Where It Is Found

Stibnite forms in low-temperature hydrothermal veins and hot-spring deposits with quartz. World-famous crystals come from the Ichinokawa Mine (Shikoku, Japan) and Romania (Baia Sprie); other sources include China (the leading producer), Bolivia, Mexico, and the western United States (Nevada, Idaho).

Frequently asked questions

How can you tell if a mineral is stibnite?

Look for steel-gray, brilliantly metallic, long striated bladed crystals that are very soft (Mohs 2), show one perfect lengthwise cleavage, give a lead-gray streak, and melt in a candle flame.

What is stibnite used for?

Stibnite (Sb2S3) is the chief ore of antimony, used in flame retardants, alloys, batteries, and historically as a cosmetic (kohl).

Stibnite vs galena: how to tell them apart?

Galena has perfect cubic cleavage and is much denser (SG ~7.5) forming cubes, while stibnite forms soft bent blades with one lengthwise cleavage and lower density (SG ~4.6).

Is stibnite dangerous to handle?

Stibnite contains antimony; avoid ingesting dust or licking specimens, wash hands after handling, and do not heat it indoors as antimony fumes are toxic.

Stibnite identified by the community

Recent Stibnite specimens identified with Rock Identifier.

Stilbite