Chrombismite is an exceptionally rare bismuth chromium oxide that typically occurs as small, dark, inconspicuous masses within hydrothermal vein deposits. Due to its rarity and dull appearance, it is primarily sought after by advanced systematic mineral collectors specializing in bismuth species. It is most famous from its type locality in the tin-rich deposits of Potosí, Bolivia.
Is this chrombismite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch chrombismite with a known reference. Chrombismite sits at Mohs 5.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: brown.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic to submetallic.
- 4Match the color rangeCompare against the expected color range: brown, orange, yellowish brown.
- 5Look at form & habitCrystal system: cubic. Typical habit: acicular, columnar.
Often confused with
Chrombismite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Chrombismite is noticeably harder (Mohs 5.5 vs. 4.5); streak differs, so Chrombismite leaves brown, Bismite leaves gray to yellow; luster reads metallic to submetallic on Chrombismite and subadamantine to dull, earthy on Bismite.
How to tell apart: Chrombismite is noticeably harder (Mohs 5.5 vs. 2.5-3.5); streak differs, so Chrombismite leaves brown, Bismutite leaves gray; luster reads metallic to submetallic on Chrombismite and vitreous, waxy, may be dull to earthy on Bismutite.
Often found alongside chrombismite
Minerals reported to co-occur with chrombismite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Bi₁₆CrO₂₇
- Mohs hardness
- 5.5
- Density
- 4.5-4.8 g/cm³
- Streak
- Brown
- Luster
- Metallic to submetallic
- Transparency
- Translucent to opaque
- Crystal system
- Cubic
- Crystal habit
- Acicular, columnar
- Cleavage
- Parting may develop along {111}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A cumulus mineral in ultramafic portions of layered mafic igneous rocks; an accessory mineral in alpine-type peridotites; also detrital
Where rockhounds find chrombismite
Classic worldwide localities
- Stillwater complex, Montana, USA
- Gassin, Var, France
- Hangha, Sierra Leone
- Tiebaghi, New Caledonia
- Economic deposits in: the Bushveld complex, Transvaal, South Africa
- Great Dyke, Zimbabwe
Field-hunting tip
Where it forms: A cumulus mineral in ultramafic portions of layered mafic igneous rocks; an accessory mineral in alpine-type peridotites; also detrital. If you start seeing olivine, enstatite, plagioclase in float, you are in the right ground. Typical habit: acicular, columnar. Train your eye for that shape before scanning the outcrop.
Common questions
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Find chrombismite on the map
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