Montroydite is a rare mercury oxide that occurs primarily as orange-red acicular needles or earthy coatings in mercury-rich deposits. It is best identified by its extreme density and close association with other mercury minerals like cinnabar in limestone environments.
Is this montroydite?
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 montroydite with a known reference. Montroydite 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. Montroydite leaves a orange streak.
- 3Read the lusterHold the specimen under a strong light. Montroydite typically shows a adamantine luster.
- 4Match the color rangeCompare against the expected color range: orange, red, brown.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: acicular crystals, earthy crusts, small prismatic forms.
Often confused with
Montroydite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside montroydite
Minerals reported to co-occur with montroydite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- HgO
- Mohs hardness
- 1.5-2
- Density
- 11.2 g/cm³
- Streak
- Orange
- Luster
- Adamantine
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Acicular Crystals, Earthy Crusts, Small Prismatic Forms
- Cleavage
- Perfect in One Direction
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Hydrothermal Veins in Limestone
- Typical price
- $50-500 thumbnail depending on crystal quality
Where rockhounds find montroydite
Classic worldwide localities
- Terlingua District, Texas, USA
- Almadén, Spain
- Idrija, Slovenia
Field-hunting tip
Look in hydrothermal veins in limestone country — that is the host setting where montroydite typically forms. If you start seeing cinnabar, calcite, native mercury in float, you are in the right ground. Field specimens usually show a acicular crystals, earthy crusts, small prismatic forms habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find montroydite on the map
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