Fukalite is a rare calcium silicate mineral primarily known from the Fuka mine in Japan. It typically occurs as white or colorless fibrous aggregates within contact metamorphic skarn zones, often associated with other rare silicate minerals.
Is this fukalite?
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 fukalite with a known reference. Fukalite sits at Mohs ~4, 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: vitreous.
- 4Match the color rangeCompare against the expected color range: white, light brown.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: crystalline.
Often confused with
Fukalite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Xonotlite is the harder of the two (Mohs 6-6.5 vs. ~4); luster reads vitreous on Fukalite and pearly, greasy on Xonotlite.
How to tell apart: Fukalite is noticeably harder (Mohs ~4 vs. 2.5).
Often found alongside fukalite
Minerals reported to co-occur with fukalite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₄Si₂O₆(CO₃)(OH)₂
- Mohs hardness
- ~4
- Density
- 2.770 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Crystalline
- Cleavage
- Perfect in one direction
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A retrograde mineral and alteration product in skarns formed from metasomatism of limestone
Where rockhounds find fukalite
Classic worldwide localities
- Fuka, near Bicchu, and Mihara, Okayama Prefecture, and at Kushiro, Hiroshima Prefecture, Japan
Field-hunting tip
Where it forms: A retrograde mineral and alteration product in skarns formed from metasomatism of limestone. If you start seeing cuspidine, xonotlite, calcite in float, you are in the right ground. Typical habit: crystalline. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify fukalite?+
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What rocks look like fukalite?+
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Find fukalite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
