Okayamalite is a very rare borosilicate mineral belonging to the melilite group, typically found as small, tabular crystals within contact metamorphic zones. It is named after the prefecture in Japan where it was first discovered. Collectors primarily seek it as a localized, exotic addition to systematic mineral collections.
Is this okayamalite?
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 okayamalite with a known reference. Okayamalite sits at Mohs 5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Okayamalite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Okayamalite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: tabular crystals, massive.
Often confused with
Okayamalite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside okayamalite
Minerals reported to co-occur with okayamalite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₂B₂SiO₇
- Mohs hardness
- 5
- Density
- 3.08 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Tetragonal
- Crystal habit
- Tabular Crystals, Massive
- Cleavage
- Poor
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Skarn
- Typical price
- $50-300 per specimen
Where rockhounds find okayamalite
Classic worldwide localities
- Fuka mine, Okayama Prefecture, Japan
Field-hunting tip
Look in skarn country — that is the host setting where okayamalite typically forms. If you start seeing gehlenite, bultfonteinite, oyelite in float, you are in the right ground. Field specimens usually show a tabular crystals, massive habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find okayamalite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
