Hillebrandite is a rare calcium silicate hydrate typically found as a result of contact metamorphism in limestone or as a hydration product of calcium silicates. It most commonly occurs in fibrous or massive aggregates and is noted for its association with other rare calcium-rich minerals in skarn deposits.
Is this hillebrandite?
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 hillebrandite with a known reference. Hillebrandite 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. Hillebrandite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Hillebrandite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, colorless, gray.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: fibrous, massive, or as veinlets.
Often confused with
Hillebrandite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Hillebrandite is noticeably harder (Mohs 6 vs. 4.5-5).
How to tell apart: Hillebrandite is noticeably harder (Mohs 6 vs. 3).
How to tell apart: Hillebrandite is noticeably harder (Mohs 6 vs. 2.5); luster reads vitreous on Hillebrandite and pearly on Tobermorite.
Often found alongside hillebrandite
Minerals reported to co-occur with hillebrandite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₂SiO₃(OH)₂
- Mohs hardness
- 6
- Density
- 2.71 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Fibrous, Massive, Or as Veinlets
- Cleavage
- Perfect in One Direction
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Metamorphosed Limestone or Calcium-rich Skarns
- Typical price
- $20-100 per specimen
Where rockhounds find hillebrandite
Classic worldwide localities
- Velardena, Mexico
- Crestmore, California, USA
- Fuka, Japan
Field-hunting tip
Look in metamorphosed limestone or calcium-rich skarns country — that is the host setting where hillebrandite typically forms. If you start seeing calcite, tobermorite, afwillite in float, you are in the right ground. Field specimens usually show a fibrous, massive, or as veinlets habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find hillebrandite on the map
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