Terlinguaite is a rare mercury halide mineral that is highly prized by collectors for its brilliant yellow color and strong fluorescence. It is typically found as small, fragile crystals in association with other mercury minerals in specific hydrothermal zones, most notably in the type locality of Terlingua, Texas.
Is this terlinguaite?
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 terlinguaite with a known reference. Terlinguaite sits at Mohs 2.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: lemon-yellow, turning olive-green.
- 3Read the lusterHold the specimen under a strong light. Luster: brilliant adamantine.
- 4Match the color rangeCompare against the expected color range: yellow, greenish yellow, brown, olive green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic, striated.
Often confused with
Terlinguaite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Terlinguaite is noticeably harder (Mohs 2.5 vs. 1.5); streak differs, so Terlinguaite leaves lemon-yellow, turning olive-green, Calomel leaves pale yellowish white; luster reads brilliant adamantine on Terlinguaite and adamantine on Calomel.
How to tell apart: Streak differs, so Terlinguaite leaves lemon-yellow, turning olive-green, Eglestonite leaves yellow or greenish yellow, rapidly becoming black.
Often found alongside terlinguaite
Minerals reported to co-occur with terlinguaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Hg₂ClO
- Mohs hardness
- 2.5
- Density
- 9.22 g/cm³
- Streak
- Lemon-yellow, turning olive-green
- Luster
- Brilliant adamantine
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic, striated
- Cleavage
- {101}, perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare secondary mineral in hydrothermal mercury deposits
Where rockhounds find terlinguaite
1 mapped spotsClassic worldwide localities
- Terlingua, Brewster Co., Texas, USA
- McDermitt mercury mine, Opalite district, and from the Cahill mine, Poverty Peak district, Humboldt Co., Nevada, USA
- Kings mine, Parkfield district, Kings Co., and the Nepper and Clear Creek mines, New Idria district, San Benito Co., California, USA
- Huahuaxtla, Guerrero, Mexico
- Pedernales, Chihuahua, Mexico
- Guadalćazar, San Luis Potosi, Mexico
Field-hunting tip
Where it forms: A rare secondary mineral in hydrothermal mercury deposits. If you start seeing cinnabar, metacinnabar, eglestonite in float, you are in the right ground. Typical habit: prismatic, striated. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Texas. Start trip planning there.
Common questions
How do you identify terlinguaite?+
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Is terlinguaite safe to handle?+
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Find terlinguaite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
