Ishikawaite is a rare, radioactive niobium-tantalum mineral found primarily in granitic pegmatites. It usually presents as black to brownish-black prismatic crystals or irregular masses, often requiring a Geiger counter for positive identification in the field.

Hardness

5-6

Mohs

Luster

Submetallic

Streak

Black

Transparency

Opaque

mineralrareSamarskite Group family

Ishikawaite

Hardness: 5-6
Luster: Submetallic
Streak: Black
Transparency: Opaque

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Is this ishikawaite?

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 ishikawaite with a known reference. Ishikawaite sits at Mohs 5-6 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Ishikawaite leaves a black streak.
3
Read the luster
Hold the specimen under a strong light. Ishikawaite typically shows a submetallic luster.
4
Match the color range
Compare against the expected color range: black, brownish-black.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: prismatic, massive, tabular.

Often confused with

Ishikawaite vs. its common look-alikes — and how to tell them apart in the field.

mineral

Columbium Ore

Mohs 6

How to tell apart: Streak differs — Ishikawaite leaves black, Columbium Ore leaves dark red to black.

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Often found alongside ishikawaite

Minerals reported to co-occur with ishikawaite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: (U,Fe,Y,Ca)(Nb,Ta)O₄
Mohs hardness: 5-6
Density: 6.2-6.4 g/cm³
Colors: Black Brownish-black
Streak: Black
Luster: Submetallic
Transparency: Opaque
Crystal system: Orthorhombic
Crystal habit: Prismatic, Massive, Tabular
Cleavage: None
Rarity: Rare
Uses: Collector, Research
Host rock: Granite Pegmatites
Typical price: $50-300 per specimen

Where rockhounds find ishikawaite

Classic worldwide localities

Ishikawa, Fukushima Prefecture, Japan
Norway
Canada

Field-hunting tip

Look in granite pegmatites country — that is the host setting where ishikawaite typically forms. If you start seeing microcline, quartz, zircon in float, you are in the right ground. Field specimens usually show a prismatic, massive, tabular habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify ishikawaite?+

Mohs hardness is 5-6. It typically shows a submetallic luster. The streak is black. Common colors include black, brownish-black.

Where is ishikawaite found?+

Notable localities include Ishikawa, Fukushima Prefecture, Japan; Norway; Canada.

How much is ishikawaite worth?+

Typical asking prices fall in the range of $50-300 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

Is ishikawaite safe to handle?+

This mineral is radioactive. This mineral is radioactive and contains uranium; it should be stored in a lead-lined or shielded container and handled with proper precautions, including wearing gloves and minimizing inhalation of dust. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like ishikawaite?+

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

What minerals are found with ishikawaite?+

Ishikawaite commonly co-occurs with Microcline, Quartz, Zircon, Monazite, Beryl. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does ishikawaite form in?+

Ishikawaite typically forms in granite pegmatites. Working float back to the host body is the standard way to chase a fresh occurrence.

What is ishikawaite used for?+

Ishikawaite is used in collector, research.

Find ishikawaite on the map

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