Mcconnellite is a rare copper chromium oxide mineral that occurs as small, dark, metallic tabular crystals in oxidized zones of copper deposits. It is structurally related to the delafossite group and is primarily a curiosity for advanced mineralogists and systematic collectors. Specimens are typically microscopic to thumbnail-sized and are found in very limited localities worldwide.
Is this mcconnellite?
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 mcconnellite with a known reference. Mcconnellite 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: black.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: dark red.
- 5Look at form & habitCrystal system: trigonal. Typical habit: tabular crystals.
Often confused with
Mcconnellite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside mcconnellite
Minerals reported to co-occur with mcconnellite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CuCrO₂
- Mohs hardness
- 5.5
- Density
- 5.49 g/cm³
- Colors
- Streak
- Black
- Luster
- Metallic
- Transparency
- Translucent in intergrowths with grimaldiite
- Crystal system
- Trigonal
- Crystal habit
- Tabular crystals
- Cleavage
- {0001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In fine-grained intergrowth with other chromium oxide-hydroxide minerals in alluvial cobbles
Where rockhounds find mcconnellite
Classic worldwide localities
- Merume River, Mazaruni district, Guyana (type locality)
Field-hunting tip
Where it forms: In fine-grained intergrowth with other chromium oxide-hydroxide minerals in alluvial cobbles. If you start seeing bracewellite, eskolaite, grimaldiite in float, you are in the right ground. Typical habit: tabular crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify mcconnellite?+
Where is mcconnellite found?+
Is mcconnellite safe to handle?+
What rocks look like mcconnellite?+
What minerals are found with mcconnellite?+
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Find mcconnellite on the map
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