Ichnusaite is an extremely rare thorium molybdate mineral typically found as small, thin, transparent tabular crystals. It was first discovered in the Su Seinargiu mine in Sardinia, where it occurs as a secondary mineral in oxidized hydrothermal environments alongside other rare species.
Is this ichnusaite?
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 ichnusaite with a known reference. Ichnusaite sits at Mohs 2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: pearly adamantine.
- 4Match the color rangeCompare against the expected color range: colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: thin tabular crystals.
Often confused with
Ichnusaite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Molybdite is the harder of the two (Mohs 3-4 vs. 2); luster reads pearly adamantine on Ichnusaite and adamantine on Molybdite.
How to tell apart: Streak differs, so Ichnusaite leaves white, Ferrimolybdite leaves pale yellow; luster reads pearly adamantine on Ichnusaite and adamantine to silky, earthy on Ferrimolybdite.
Often found alongside ichnusaite
Minerals reported to co-occur with ichnusaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Th(MoO₄)₂·3H₂O
- Mohs hardness
- 2
- Density
- 4.262 g/cm³
- Colors
- Streak
- White
- Luster
- Pearly adamantine
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Thin tabular crystals
- Cleavage
- Perfect on {100}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary mineral in vugs in hydrothermal veins cutting porphyritic granite
Where rockhounds find ichnusaite
Classic worldwide localities
- Su Seinargiu, southwest of Sarroch, Cagliari, Sardinia, Italy
Field-hunting tip
Where it forms: A secondary mineral in vugs in hydrothermal veins cutting porphyritic granite. If you start seeing nuragheite, muscovite, xenotime- in float, you are in the right ground. Typical habit: thin tabular crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ichnusaite?+
Where is ichnusaite found?+
Is ichnusaite safe to handle?+
What rocks look like ichnusaite?+
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Find ichnusaite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
