Comancheite is a rare mercury halide mineral found almost exclusively in the mercury mines of the Terlingua district in Texas. It typically presents as distinct, vibrant orange to reddish-orange platy crystals or granular masses associated with other rare mercury minerals.
Is this comancheite?
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 comancheite with a known reference. Comancheite sits at Mohs 2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: yellow-orange.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous in crystals; resinous when massive.
- 4Match the color rangeCompare against the expected color range: yellow, orange red, red.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: acicular, stellate.
Often confused with
Comancheite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Comancheite leaves yellow-orange, Eglestonite leaves yellow or greenish yellow, rapidly becoming black; luster reads vitreous in crystals; resinous when massive on Comancheite and brilliant adamantine to resinous on Eglestonite.
How to tell apart: Kleinite is the harder of the two (Mohs 3.5-4 vs. 2); streak differs, so Comancheite leaves yellow-orange, Kleinite leaves sulfur-yellow; luster reads vitreous in crystals; resinous when massive on Comancheite and adamantine to greasy on Kleinite.
How to tell apart: Streak differs, so Comancheite leaves yellow-orange, Terlinguaite leaves lemon-yellow, turning olive-green; luster reads vitreous in crystals; resinous when massive on Comancheite and brilliant adamantine on Terlinguaite.
Often found alongside comancheite
Minerals reported to co-occur with comancheite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Hg₅₅N₂₄(NH₂,OH)₄(Cl,Br)₃₄
- Mohs hardness
- 2
- Density
- 7.7 g/cm³
- Colors
- Streak
- Yellow-orange
- Luster
- Vitreous in crystals; resinous when massive
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Acicular, stellate
- Cleavage
- Fair on {001} and {110}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary mineral in an oxidized mercury deposit
Where rockhounds find comancheite
Classic worldwide localities
- Mariposa mine, Terlingua, Brewster Co., Texas, USA
Field-hunting tip
Where it forms: A secondary mineral in an oxidized mercury deposit. If you start seeing calcite, goethite, hematite in float, you are in the right ground. Typical habit: acicular, stellate. Train your eye for that shape before scanning the outcrop.
Common questions
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Find comancheite on the map
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