Kimuraite-(Y) is an extremely rare yttrium calcium carbonate mineral typically found in small, thin platy crystals. It is most notable for occurring primarily in specific alkaline igneous environments in Japan. Due to its scarcity, it is considered a premier prize for advanced rare-earth mineral collectors.

Hardness

3.5

Mohs

Luster

Pearly

Streak

White

Transparency

Translucent

mineralrareTengerite Group family

Kimuraite-(Y)

Hardness: 3.5
Luster: Pearly
Streak: White
Transparency: Translucent

Is this kimuraite-(y)?

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 kimuraite-(y) with a known reference. Kimuraite-(Y) sits at Mohs 3.5 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Kimuraite-(Y) leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Kimuraite-(Y) typically shows a pearly luster.
4
Match the color range
Compare against the expected color range: pink, white, colorless.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: platy crystals.

Often confused with

Kimuraite-(Y) vs. its common look-alikes — and how to tell them apart in the field.

mineral

Tengerite-(Y)

Mohs 3.5

How to tell apart: Luster reads pearly on Kimuraite-(Y) and dull on Tengerite-(Y).

Often found alongside kimuraite-(y)

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

All properties

Chemical formula: CaY₂ (CO₃)₄·6H₂O
Mohs hardness: 3.5
Density: 3.9 g/cm³
Colors: Pink White Colorless
Streak: White
Luster: Pearly
Transparency: Translucent
Crystal system: Orthorhombic
Crystal habit: Platy Crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Alkaline Igneous Rocks
Typical price: $50-300 per micro-specimen

Where rockhounds find kimuraite-(y)

Classic worldwide localities

Hosei, Karasawa, Nagano Prefecture, Japan

Field-hunting tip

Look in alkaline igneous rocks country — that is the host setting where kimuraite-(y) typically forms. If you start seeing calcite, quartz, ancylite-(ce) in float, you are in the right ground. Field specimens usually show a platy crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify kimuraite-(y)?+

Mohs hardness is 3.5. It typically shows a pearly luster. The streak is white. Common colors include pink, white, colorless.

Where is kimuraite-(y) found?+

Notable localities include Hosei, Karasawa, Nagano Prefecture, Japan.

How much is kimuraite-(y) worth?+

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

What rocks look like kimuraite-(y)?+

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

What minerals are found with kimuraite-(y)?+

Kimuraite-(Y) commonly co-occurs with Calcite, Quartz, Ancylite-(Ce). Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does kimuraite-(y) form in?+

Kimuraite-(Y) typically forms in alkaline igneous rocks. Working float back to the host body is the standard way to chase a fresh occurrence.

What is kimuraite-(y) used for?+

Kimuraite-(Y) is used in collector.

Find kimuraite-(y) on the map

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