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 4 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Chrombismite leaves a brownish black streak.
- 3Read the lusterHold the specimen under a strong light. Chrombismite typically shows a submetallic luster.
- 4Match the color rangeCompare against the expected color range: dark brown, black.
- 5Look at form & habitCrystal system: cubic. Typical habit: massive, anhedral grains.
Often confused with
Chrombismite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Chrombismite leaves brownish black, Bismite leaves white; luster reads submetallic on Chrombismite and adamantine on Bismite.
How to tell apart: Chrombismite is noticeably harder (Mohs 4 vs. 3); streak differs — Chrombismite leaves brownish black, Bismutite leaves white; luster reads submetallic on Chrombismite and pearly 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
- Bi₂CrO₆
- Mohs hardness
- 4
- Density
- 9.2 g/cm³
- Colors
- Streak
- Brownish Black
- Luster
- Submetallic
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Massive, Anhedral Grains
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Hydrothermal Veins
- Typical price
- $100-500 per specimen
Where rockhounds find chrombismite
Classic worldwide localities
- Tasna Mine, Potosí, Bolivia
- San Francisco Mine, Bolivia
Field-hunting tip
Look in hydrothermal veins country — that is the host setting where chrombismite typically forms. If you start seeing bismutite, bismite, cassiterite in float, you are in the right ground. Field specimens usually show a massive, anhedral grains habit, so 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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