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.

Hardness

2.5

Mohs

Luster

Adamantine

Streak

Yellow

Transparency

Translucent

mineralrare

Comancheite

Hardness: 2.5
Luster: Adamantine
Streak: Yellow
Transparency: Translucent

Is this comancheite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch comancheite with a known reference. Comancheite sits at Mohs 2.5 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Comancheite leaves a yellow streak.
3
Read the luster
Hold the specimen under a strong light. Comancheite typically shows a adamantine luster.
4
Match the color range
Compare against the expected color range: orange, reddish-orange, yellow.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: platy crystals, granular aggregates.

Often confused with

Comancheite vs. its common look-alikes — and how to tell them apart in the field.

mineral

Eglestonite

Mohs 2.5

How to tell apart: Streak differs — Comancheite leaves yellow, Eglestonite leaves yellowish-white.

How to tell apart: Kleinite is the harder of the two (Mohs 3.5 vs. 2.5); streak differs — Comancheite leaves yellow, Kleinite leaves white.

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: Hg₅(Cl,Br)₂(O,OH)₃
Mohs hardness: 2.5
Density: 7.52 g/cm³
Colors: Orange Reddish-orange Yellow
Streak: Yellow
Luster: Adamantine
Transparency: Translucent
Crystal system: Orthorhombic
Crystal habit: Platy Crystals, Granular Aggregates
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Mercury-bearing Hydrothermal Veins
Typical price: $50-300 per specimen depending on size and quality

Where rockhounds find comancheite

Classic worldwide localities

Terlingua District, Texas, USA

Field-hunting tip

Look in mercury-bearing hydrothermal veins country — that is the host setting where comancheite typically forms. If you start seeing calomel, cinnabar, montroydite in float, you are in the right ground. Field specimens usually show a platy crystals, granular aggregates habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify comancheite?+

Mohs hardness is 2.5. It typically shows a adamantine luster. The streak is yellow. Common colors include orange, reddish-orange, yellow.

Where is comancheite found?+

Notable localities include Terlingua District, Texas, USA.

How much is comancheite worth?+

Typical asking prices fall in the range of $50-300 per specimen depending on size and quality. Quality, size, and provenance can move individual specimens well outside that range.

Is comancheite safe to handle?+

It contains toxic constituents. Comancheite contains significant amounts of mercury. Handle with care, wash hands thoroughly after contact, and keep in a sealed, labeled container away from living spaces to avoid dust inhalation. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like comancheite?+

Comancheite is most often confused with Eglestonite, Kleinite, Terlinguaite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with comancheite?+

Comancheite commonly co-occurs with Calomel, Cinnabar, Montroydite, Eglestonite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does comancheite form in?+

Comancheite typically forms in mercury-bearing hydrothermal veins. Working float back to the host body is the standard way to chase a fresh occurrence.

What is comancheite used for?+

Comancheite is used in collector.

Find comancheite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.