Idrialite is a rare organic mineral composed of a polycyclic aromatic hydrocarbon found in mercury mines. It is most famous for its distinctive and striking bright blue fluorescence under long-wave ultraviolet light, which makes it highly sought after by mineral collectors.
Is this idrialite?
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 idrialite with a known reference. Idrialite sits at Mohs 1-2 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Idrialite leaves a yellowish-white streak.
- 3Read the lusterHold the specimen under a strong light. Idrialite typically shows a resinous luster.
- 4Match the color rangeCompare against the expected color range: yellow, yellow-white, greenish-yellow.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: massive, granular, or fine-grained aggregates.
Often confused with
Idrialite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Idrialite leaves yellowish-white, Sulfur leaves white.
How to tell apart: Streak differs — Idrialite leaves yellowish-white, Orpiment leaves yellow.
How to tell apart: Streak differs — Idrialite leaves yellowish-white, Cinnabar leaves scarlet; luster reads resinous on Idrialite and adamantine on Cinnabar.
Often found alongside idrialite
Minerals reported to co-occur with idrialite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- C₂₂H₁₄
- Mohs hardness
- 1-2
- Density
- 1.4 g/cm³
- Streak
- Yellowish-white
- Luster
- Resinous
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Massive, Granular, Or Fine-grained Aggregates
- Cleavage
- None
- Fluorescence
- Bright Blue Under UV Light
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Mercury-bearing Hydrothermal Deposits and Bituminous Shales
- Typical price
- $50-300 per specimen
Where rockhounds find idrialite
Classic worldwide localities
- Idrija, Slovenia
- Terlingua, Texas, USA
Field-hunting tip
Look in mercury-bearing hydrothermal deposits and bituminous shales country — that is the host setting where idrialite typically forms. If you start seeing cinnabar, mercury, pyrite in float, you are in the right ground. Field specimens usually show a massive, granular, or fine-grained aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find idrialite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
