Cairncrossite is a rare strontium-calcium silicate that typically forms as delicate, pearly-white radiating aggregates. It is primarily found within the manganese-rich environments of the Kalahari Manganese Field, often appearing as distinct micro-crystals associated with other rare hydrothermal minerals.

Hardness

Mohs

Luster

Pearly

Streak

White

Transparency

Transparent

mineralrareTobermorite Group family

Cairncrossite

Hardness: 3
Luster: Pearly
Streak: White
Transparency: Transparent

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Is this cairncrossite?

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 cairncrossite with a known reference. Cairncrossite sits at Mohs 3 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Cairncrossite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Cairncrossite typically shows a pearly luster.
4
Match the color range
Compare against the expected color range: white, colorless.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: platy crystals, radial aggregates.

Often confused with

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

How to tell apart: Apophyllite is the harder of the two (Mohs 4.5-5 vs. 3); luster reads pearly on Cairncrossite and vitreous to pearly on Apophyllite.

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Often found alongside cairncrossite

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

All properties

Chemical formula: (Sr,Ca)₁₄(Si₄O₁₀)₂(Si₂O₇)(OH)₄·~20H₂O
Mohs hardness: 3
Density: 2.16 g/cm³
Colors: White Colorless
Streak: White
Luster: Pearly
Transparency: Transparent
Crystal system: Orthorhombic
Crystal habit: Platy Crystals, Radial Aggregates
Cleavage: Perfect
Rarity: Rare
Uses: Collector
Host rock: Hydrothermal Veins in Manganese Ore Deposits
Typical price: $50-300 per specimen

Where rockhounds find cairncrossite

Classic worldwide localities

Kalahari Manganese Field, South Africa

Field-hunting tip

Look in hydrothermal veins in manganese ore deposits country — that is the host setting where cairncrossite typically forms. If you start seeing manganite, hausmannite, calcite in float, you are in the right ground. Field specimens usually show a platy crystals, radial aggregates habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify cairncrossite?+

Mohs hardness is 3. It typically shows a pearly luster. The streak is white. Common colors include white, colorless.

Where is cairncrossite found?+

Notable localities include Kalahari Manganese Field, South Africa.

How much is cairncrossite worth?+

Typical asking prices fall in the range of $50-300 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like cairncrossite?+

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

What minerals are found with cairncrossite?+

Cairncrossite commonly co-occurs with Manganite, Hausmannite, Calcite, Baryte. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does cairncrossite form in?+

Cairncrossite typically forms in hydrothermal veins in manganese ore deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is cairncrossite used for?+

Cairncrossite is used in collector.

Find cairncrossite on the map

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