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.

Hardness

5-6

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent to translucent

mineralrare

Hillebrandite

Hardness: 5-6
Luster: Vitreous
Streak: White
Transparency: Transparent to translucent

Is this hillebrandite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch hillebrandite with a known reference. Hillebrandite sits at Mohs 5-6, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: white, colorless, greenish white.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: fibrous, radial.

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 5-6 vs. 3-4).

How to tell apart: Hillebrandite is noticeably harder (Mohs 5-6 vs. 2.5).

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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: 5-6
Density: 2.66-2.69 g/cm³
Colors: White Colorless Greenish white
Streak: White
Luster: Vitreous
Transparency: Transparent to translucent
Crystal system: Orthorhombic
Crystal habit: Fibrous, radial
Cleavage: {010}
Rarity: Rare
Uses: Collector
Host rock: In limestone affected by high-grade contact metamorphism

Where rockhounds find hillebrandite

Classic worldwide localities

Crestmore, Riverside Co., California, USA
Terneras mine, Velardeña, Durango, Mexico
Carlingford, Co. Louth, Ireland
Güneyce-_ Ikizdere area, Trabzon Province, Turkey
Mt. Chapchachi, north of the Caspian Sea, Kazakhstan
Nugrah, Saudi Arabia

Field-hunting tip

Where it forms: In limestone affected by high-grade contact metamorphism. If you start seeing wollastonite, garnet, calcite in float, you are in the right ground. Typical habit: fibrous, radial. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify hillebrandite?+

Mohs hardness is 5-6. Luster: vitreous. The streak is white. Common colors include white, colorless, greenish white.

Where is hillebrandite found?+

Notable localities include Crestmore, Riverside Co., California, USA; Terneras mine, Velardeña, Durango, Mexico; Carlingford, Co. Louth, Ireland; Güneyce-_ Ikizdere area, Trabzon Province, Turkey; Mt. Chapchachi, north of the Caspian Sea, Kazakhstan.

What rocks look like hillebrandite?+

Hillebrandite is most often confused with Wollastonite, Afwillite, Tobermorite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with hillebrandite?+

Hillebrandite commonly co-occurs with Wollastonite, Garnet, Calcite, Vesuvianite, Grossular, Foshagite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does hillebrandite form in?+

Where it forms: In limestone affected by high-grade contact metamorphism. Working float back to the host body is the standard way to chase a fresh occurrence.

What is hillebrandite used for?+

Hillebrandite is used in collector.

Find hillebrandite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.