Calomel is a rare secondary mercury chloride mineral typically found in the oxidation zones of mercury-bearing ore deposits. It is known for its high density and characteristic adamantine luster, often appearing as crusts or small, poorly formed crystals associated with native mercury and cinnabar.
Is this calomel?
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 calomel with a known reference. Calomel sits at Mohs 1.5-2 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Calomel leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Calomel typically shows a adamantine luster.
- 4Match the color rangeCompare against the expected color range: white, yellowish-white, gray, brown.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: prismatic crystals, massive, earthy, crusts.
Often confused with
Calomel vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside calomel
Minerals reported to co-occur with calomel. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Hg₂Cl₂
- Mohs hardness
- 1.5-2
- Density
- 6.49 g/cm³
- Streak
- White
- Luster
- Adamantine
- Transparency
- Translucent
- Crystal system
- Tetragonal
- Crystal habit
- Prismatic Crystals, Massive, Earthy, Crusts
- Cleavage
- Distinct On {101}
- Fluorescence
- Strong Orange Under UV
- Rarity
- Rare
- Uses
- Collector, Scientific Research
- Host rock
- Hydrothermal Mercury Deposits
- Typical price
- $50-300+ per specimen
Where rockhounds find calomel
1 mapped spotsClassic worldwide localities
- Moschellandsberg, Germany
- Almaden, Spain
- Terlingua, Texas, USA
- Idrija, Slovenia
Field-hunting tip
Look in hydrothermal mercury deposits country — that is the host setting where calomel typically forms. If you start seeing cinnabar, native mercury, calcite in float, you are in the right ground. Field specimens usually show a prismatic crystals, massive, earthy, crusts habit, so 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
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Find calomel on the map
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