Numanoite is an extremely rare copper-bearing borosilicate mineral first discovered in Japan. It typically occurs as small tabular crystals within skarn deposits and is highly prized by advanced mineral collectors for its unique chemistry.

Hardness

4.5

Mohs

Luster

Vitreous

Streak

White to pale blue-green

Transparency

Translucent

mineralrareDatolite Group family

Numanoite

Hardness: 4.5
Luster: Vitreous
Streak: White to pale blue-green
Transparency: Translucent

Is this numanoite?

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 numanoite with a known reference. Numanoite sits at Mohs 4.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white to pale blue-green.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: colorless, blue green.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: inclusions.

Often confused with

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

How to tell apart: Gadolinite-(Y) is the harder of the two (Mohs 6.5-7 vs. 4.5); streak differs, so Numanoite leaves white to pale blue-green, Gadolinite-(Y) leaves greenish gray.

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Often found alongside numanoite

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

All properties

Chemical formula: Ca₄CuB₄O₆(OH)₆(CO₃)₂
Mohs hardness: 4.5
Density: 2.96 g/cm³
Colors: Colorless Blue green
Streak: White to pale blue-green
Luster: Vitreous
Transparency: Translucent
Crystal system: Monoclinic
Crystal habit: Inclusions
Cleavage: Perfect, in two directions
Rarity: Rare
Uses: Collector
Host rock: On the wall of cavities in a vein of nifontovite or in fractures in a crystalline limestone near gehlenite-spurrite skarns

Where rockhounds find numanoite

Classic worldwide localities

Fuka Mine, Okayama Prefecture, Japan

Field-hunting tip

Where it forms: On the wall of cavities in a vein of nifontovite or in fractures in a crystalline limestone near gehlenite-spurrite skarns. If you start seeing borcarite, nifontovite, bultfonteinite in float, you are in the right ground. Typical habit: inclusions. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify numanoite?+

Mohs hardness is 4.5. Luster: vitreous. The streak is white to pale blue-green. Common colors include colorless, blue green.

Where is numanoite found?+

Notable localities include Fuka Mine, Okayama Prefecture, Japan.

Is numanoite safe to handle?+

Numanoite contains copper. Wash your hands afterwards, never grind or breathe the dust, and store it apart from specimens you handle often.

What rocks look like numanoite?+

Numanoite is most often confused with Datolite, Gadolinite-(Y). A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with numanoite?+

Numanoite commonly co-occurs with Borcarite, Nifontovite, Bultfonteinite, Calcite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does numanoite form in?+

Where it forms: On the wall of cavities in a vein of nifontovite or in fractures in a crystalline limestone near gehlenite-spurrite skarns. Working float back to the host body is the standard way to chase a fresh occurrence.

What is numanoite used for?+

Numanoite is used in collector.

Find numanoite on the map

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