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 ~5.5, 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: earthy.
- 4Match the color rangeCompare against the expected color range: creamy white.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: microscopic crystals.
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
- ~5.5
- Density
- 3.3 g/cm³
- Colors
- Creamy white
- Streak
- White
- Luster
- Earthy
- Transparency
- Translucent
- Crystal system
- Tetragonal
- Crystal habit
- Microscopic crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In skarn by boron metasomatism of a wollastonite-calcite aggregate (Japan); probably by desilication-dehydroxylation of datolite in a magnetite-hematite skarn deposit (Norway)
Where rockhounds find okayamalite
Classic worldwide localities
- Fuka Mine, Bicchu-cho, Okayama Prefecture, Japan (type locality)
- Arendal district, Sørlandet, Norway
Field-hunting tip
Where it forms: In skarn by boron metasomatism of a wollastonite-calcite aggregate (Japan); probably by desilication-dehydroxylation of datolite in a magnetite-hematite skarn deposit (Norway). If you start seeing wollastonite, vesuvianite, calcite in float, you are in the right ground. Typical habit: microscopic crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify okayamalite?+
Where is okayamalite found?+
What rocks look like okayamalite?+
What minerals are found with okayamalite?+
What kind of rock does okayamalite form in?+
What is okayamalite used for?+
Find okayamalite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
