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.

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, 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.