Guyanaite is a rare chromium oxyhydroxide mineral typically found as tiny, dark green to black platy crystals. It is primarily identified in weathered chromium-rich deposits and requires microscopic examination for positive identification.
Is this guyanaite?
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 guyanaite with a known reference. Guyanaite sits at Mohs 3-4 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Guyanaite leaves a light green streak.
- 3Read the lusterHold the specimen under a strong light. Guyanaite typically shows a submetallic luster.
- 4Match the color rangeCompare against the expected color range: dark green, black.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: platy, granular.
Often confused with
Guyanaite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Iron Ore is the harder of the two (Mohs 5-6.5 vs. 3-4); streak differs — Guyanaite leaves light green, Iron Ore leaves reddish-brown to black; luster reads submetallic on Guyanaite and metallic to submetallic on Iron Ore.
How to tell apart: Lepidocrocite is the harder of the two (Mohs 5 vs. 3-4); streak differs — Guyanaite leaves light green, Lepidocrocite leaves orange-red.
Often found alongside guyanaite
Minerals reported to co-occur with guyanaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CrO(OH)
- Mohs hardness
- 3-4
- Density
- 4.2-4.5 g/cm³
- Colors
- Streak
- Light Green
- Luster
- Submetallic
- Transparency
- Opaque
- Crystal system
- Tetragonal
- Crystal habit
- Platy, Granular
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Weathered Chromitite Deposits
- Typical price
- $100-500 for small specimen
Where rockhounds find guyanaite
Classic worldwide localities
- Guyana
- Turkey
- Russia
Field-hunting tip
Look in weathered chromitite deposits country — that is the host setting where guyanaite typically forms. If you start seeing goethite, chromite, quartz in float, you are in the right ground. Field specimens usually show a platy, granular habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find guyanaite on the map
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