Dellaite is a rare calcium silicate mineral typically found in high-temperature contact metamorphic environments, such as altered limestone xenoliths in igneous rocks. Collectors primarily look for it as platy, colorless-to-white crystal aggregates associated with other rare calcium-silicate species.
Is this dellaite?
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 dellaite with a known reference. Dellaite sits at Mohs 3.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: colorless.
- 5Look at form & habitCrystal system: triclinic. Typical habit: platy crystals, granular, massive.
Often confused with
Dellaite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Rankinite is the harder of the two (Mohs 5.5 vs. 3.5).
How to tell apart: Kilchoanite is the harder of the two (Mohs 5 vs. 3.5).
How to tell apart: Luster reads vitreous on Dellaite and dull on Tilleyite.
Often found alongside dellaite
Minerals reported to co-occur with dellaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₆(Si₂O₇)(SiO₄)(OH)₂
- Mohs hardness
- 3.5
- Density
- 2.94 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Platy crystals, granular, massive
- Cleavage
- Perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In late-stage, fracture-controlled replacement veins cutting thermally metamorphosed limestones (Scotland)
Where rockhounds find dellaite
Classic worldwide localities
- Kilchoan, Ardnamurchan, Argyllshire, Scotland, Japan
- Akagane mine, Kitakami Mountains, Iwate Prefecture, Honshu island, Japan
- Rize region, Eastern Pontides Turkey, Russia
- Birkhin gabbro massif, Eastern Siberia, Russia
Field-hunting tip
Where it forms: In late-stage, fracture-controlled replacement veins cutting thermally metamorphosed limestones (Scotland). If you start seeing calcite, spurrite, kilchoanite in float, you are in the right ground. Typical habit: platy crystals, granular, massive. Train your eye for that shape before scanning the outcrop.
Common questions
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Find dellaite on the map
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