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, 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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