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.

Hardness

Mohs

Luster

Pearly

Streak

White

Transparency

Transparent

mineralrare

Ichnusaite

Hardness: 2
Luster: Pearly
Streak: White
Transparency: Transparent

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Is this ichnusaite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch ichnusaite with a known reference. Ichnusaite sits at Mohs 2 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Ichnusaite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Ichnusaite typically shows a pearly luster.
4
Match the color range
Compare against the expected color range: yellow, colorless.
5
Look at form & habit
Crystal 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.

mineral

Molybdite

Mohs 1-2

How to tell apart: Streak differs — Ichnusaite leaves white, Molybdite leaves yellow; luster reads pearly on Ichnusaite and silky on Molybdite.

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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: 5.68 g/cm³
Colors: Yellow Colorless
Streak: White
Luster: Pearly
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Thin Tabular Crystals
Cleavage: Perfect in One Direction
Rarity: Rare
Uses: Collector
Host rock: Oxidized Zones of Hydrothermal Ore Deposits
Typical price: $200-1000+ for micro-specimens

Where rockhounds find ichnusaite

Classic worldwide localities

Su Seinargiu mine, Sarroch, Sardinia, Italy

Field-hunting tip

Look in oxidized zones of hydrothermal ore deposits country — that is the host setting where ichnusaite typically forms. If you start seeing nuragheite, saite, quartz in float, you are in the right ground. Field specimens usually show a thin tabular crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify ichnusaite?+

Mohs hardness is 2. It typically shows a pearly luster. The streak is white. Common colors include yellow, colorless.

Where is ichnusaite found?+

Notable localities include Su Seinargiu mine, Sarroch, Sardinia, Italy.

How much is ichnusaite worth?+

Typical asking prices fall in the range of $200-1000+ for micro-specimens. Quality, size, and provenance can move individual specimens well outside that range.

Is ichnusaite safe to handle?+

This mineral is radioactive. Contains thorium, which is radioactive. Handle with gloves and wash hands thoroughly after contact; store away from other minerals to prevent cross-contamination. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like ichnusaite?+

Ichnusaite is most often confused with Molybdite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with ichnusaite?+

Ichnusaite commonly co-occurs with Nuragheite, Saite, Quartz, Goethite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does ichnusaite form in?+

Ichnusaite typically forms in oxidized zones of hydrothermal ore deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is ichnusaite used for?+

Ichnusaite is used in collector.

Find ichnusaite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.