Wiluite is a rare borosilicate mineral that is structurally related to vesuvianite, often appearing as distinct, lustrous yellow-green to brown prismatic crystals. It is primarily found in contact metamorphic zones where boron-rich fluids have interacted with limestone. Collectors highly prize these crystals for their sharp tetragonal habit and distinct chemical composition compared to common vesuvianite.
Is this wiluite?
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 wiluite with a known reference. Wiluite sits at Mohs 6 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Wiluite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Wiluite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: yellow, green, brown.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: prismatic crystals.
Often confused with
Wiluite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside wiluite
Minerals reported to co-occur with wiluite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₁₉Mg₃Al₄(B,Al,Fe)₅Si₁₈O₆₉(OH,O)₉
- Mohs hardness
- 6
- Density
- 3.37-3.41 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Tetragonal
- Crystal habit
- Prismatic Crystals
- Cleavage
- Poor
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Contact Metamorphosed Limestone
- Typical price
- $20-150 for thumbnail to small cabinet specimens
Where rockhounds find wiluite
Classic worldwide localities
- Wilui River, Sakha Republic, Russia
- Holt Quarry, Quebec, Canada
- Eden Mills, Vermont, USA
Field-hunting tip
Look in contact metamorphosed limestone country — that is the host setting where wiluite typically forms. If you start seeing grossular, diopside, calcite in float, you are in the right ground. Field specimens usually show a prismatic crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find wiluite on the map
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