Katoite is a rare member of the garnet group that contains significant amounts of structural hydroxyl groups. It is typically found as small, white to colorless dodecahedral crystals in volcanic contact zones and metamorphosed limestone environments.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrareGarnet Group family

Katoite

Hardness: 6
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this katoite?

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 katoite with a known reference. Katoite sits at Mohs 6 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Katoite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Katoite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: white, colorless, pale yellow.
5
Look at form & habit
Crystal system: isometric. Typical habit: dodecahedral crystals, massive.

Often confused with

Katoite vs. its common look-alikes — and how to tell them apart in the field.

Often found alongside katoite

Minerals reported to co-occur with katoite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: Ca₃Al₂(SiO₄)₃₋ₓ(OH)₄ₓ
Mohs hardness: 6
Density: 2.8 g/cm³
Colors: White Colorless Pale Yellow
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Isometric
Crystal habit: Dodecahedral Crystals, Massive
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Metamorphosed Limestone Inclusions in Volcanic Rocks
Typical price: $20-150 for micro-crystals

Where rockhounds find katoite

Classic worldwide localities

Caspar quarry, Germany
Cretaceous limestones, Italy
Mont Saint-Hilaire, Canada

Field-hunting tip

Look in metamorphosed limestone inclusions in volcanic rocks country — that is the host setting where katoite typically forms. If you start seeing ettringite, afwillite, calcite in float, you are in the right ground. Field specimens usually show a dodecahedral crystals, massive habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify katoite?+

Mohs hardness is 6. It typically shows a vitreous luster. The streak is white. Common colors include white, colorless, pale yellow.

Where is katoite found?+

Notable localities include Caspar quarry, Germany; Cretaceous limestones, Italy; Mont Saint-Hilaire, Canada.

How much is katoite worth?+

Typical asking prices fall in the range of $20-150 for micro-crystals. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like katoite?+

Katoite is most often confused with Grossularite Garnet. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with katoite?+

Katoite commonly co-occurs with Ettringite, Afwillite, Calcite, Tobermorite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does katoite form in?+

Katoite typically forms in metamorphosed limestone inclusions in volcanic rocks. Working float back to the host body is the standard way to chase a fresh occurrence.

What is katoite used for?+

Katoite is used in collector.

Find katoite on the map

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