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.

Hardness

3.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Dellaite

Hardness: 3.5
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this dellaite?

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 dellaite with a known reference. Dellaite sits at Mohs 3.5 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Dellaite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Dellaite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: colorless, white, grayish.
5
Look at form & habit
Crystal 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.

mineral

Rankinite

Mohs 5.5

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).

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: Ca₆Si₃O₁₀(OH)₂
Mohs hardness: 3.5
Density: 2.95 g/cm³
Colors: Colorless White Grayish
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Triclinic
Crystal habit: Platy Crystals, Granular, Massive
Cleavage: Perfect
Rarity: Rare
Uses: Collector
Host rock: Metamorphosed Limestone (skarn Zones)
Typical price: $50-300 per specimen

Where rockhounds find dellaite

Classic worldwide localities

Ballycraigy, Northern Ireland
Fuka, Japan
Halamish, Israel

Field-hunting tip

Look in metamorphosed limestone (skarn zones) country — that is the host setting where dellaite typically forms. If you start seeing calcite, ettringite, afwillite in float, you are in the right ground. Field specimens usually show a platy crystals, granular, massive habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify dellaite?+

Mohs hardness is 3.5. It typically shows a vitreous luster. The streak is white. Common colors include colorless, white, grayish.

Where is dellaite found?+

Notable localities include Ballycraigy, Northern Ireland; Fuka, Japan; Halamish, Israel.

How much is dellaite 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 dellaite?+

Dellaite is most often confused with Rankinite, Kilchoanite, Tilleyite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with dellaite?+

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

What kind of rock does dellaite form in?+

Dellaite typically forms in metamorphosed limestone (skarn zones). Working float back to the host body is the standard way to chase a fresh occurrence.

What is dellaite used for?+

Dellaite is used in collector.

Find dellaite on the map

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