Stibnite
Sb₂S₃ · Orthorhombic · also called antimony glance
Stibnite is the main ore of antimony and one of the most striking metallic minerals a collector can own — long steel-grey blades that look almost manufactured. It is very soft and very easily damaged, which is why undamaged specimens command high prices.
Properties
- Mohs hardness
- 2
- Streak
- lead gray
- Lustre
- metallic
- Colour
- Bright silvery lead-grey when fresh, often tarnishing to a dull black or developing an iridescent film.
- Cleavage
- Perfect cleavage along the length of the crystal, which is why stibnite blades so often end up bent or split.
- Fracture
- Subconchoidal, but cleavage dominates
- Specific gravity
- 4.6–4.7 (water = 1)
- Magnetism
- Not magnetic
- Acid test
- No reaction
- UV
- Not fluorescent
Tests that confirm stibnite
- Slender, steely blades and needles, frequently bent or splayed into sprays — a habit nothing else common matches.
- Very soft. A fingernail marks it, and it can be cut with a knife like lead.
- Melts in a match flame, which is unusual enough to be diagnostic.
What stibnite gets confused with
Each of these is settled by one test. Run that test first.
Galena breaks into cubes and is far heavier. Stibnite forms blades and splits along their length.
Molybdenite peels into greasy flexible sheets; stibnite splinters into blades.
Where it is found
Low-temperature hydrothermal veins and hot spring deposits. The finest specimens by a wide margin come from Ichinokawa in Japan and from Hunan Province in China.
Is it worth anything?
Common massive material is inexpensive. Large undamaged crystal sprays are among the more valuable mineral specimens on the market. Antimony compounds are toxic — wash your hands.