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 1-1.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: yellowish-white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to adamantine.
- 4Match the color rangeCompare against the expected color range: greenish yellow, light brown, colorless.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: tabular.
Often confused with
Idrialite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Idrialite leaves yellowish-white, Sulfur leaves white; luster reads vitreous to adamantine on Idrialite and resinous on Sulfur.
How to tell apart: Streak differs, so Idrialite leaves yellowish-white, Orpiment leaves pale lemon-yellow; luster reads vitreous to adamantine on Idrialite and resinous, pearly on cleavage surface on Orpiment.
How to tell apart: Streak differs, so Idrialite leaves yellowish-white, Cinnabar leaves scarlet; luster reads vitreous to adamantine on Idrialite and adamantine, inclining to metallic when dark; dull in friable material 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
- 1-1.5
- Density
- 1.22-1.236 g/cm³
- Streak
- Yellowish-white
- Luster
- Vitreous to adamantine
- Transparency
- Semitransparent
- Crystal system
- Orthorhombic
- Crystal habit
- Tabular
- Cleavage
- {001}, perfect; {100}, poor
- Fluorescence
- Blue under SW and LW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Probably formed by pyrolysis of organic material near hot springs or by hydrothermal fluids
Where rockhounds find idrialite
Classic worldwide localities
- Skaggs Springs, Sonoma Co., California, USA
- Great Western, Mirabel, Helen, and Research mines, Lake Co., California, USA
- Knoxville mine, Napa Co, California, USA
- Idrija (Idria) mercury mine, 38 km west of Ljubljana, northwestern Slovenia
Field-hunting tip
Where it forms: Probably formed by pyrolysis of organic material near hot springs or by hydrothermal fluids. If you start seeing cinnabar, pyrite, gypsum in float, you are in the right ground. Typical habit: tabular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify idrialite?+
Where is idrialite found?+
Is idrialite safe to handle?+
What rocks look like idrialite?+
What minerals are found with idrialite?+
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Find idrialite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
