Killalaite is a rare calcium silicate mineral typically found in contact metamorphic limestone deposits. It is most frequently encountered as small, colorless platy crystals associated with calc-silicate skarns, making it a highly sought-after species for mineralogists and advanced collectors.

Hardness

5.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Translucent

mineralrare

Killalaite

Hardness: 5.5
Luster: Vitreous
Streak: White
Transparency: Translucent

Is this killalaite?

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 killalaite with a known reference. Killalaite sits at Mohs 5.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Killalaite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Killalaite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: colorless, white.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: platy crystals, granular aggregates.

Often confused with

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

mineral

Calcite

Mohs 3

How to tell apart: Killalaite is noticeably harder (Mohs 5.5 vs. 3).

Often found alongside killalaite

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

All properties

Chemical formula: Ca₆Si₂O₇(OH)₂
Mohs hardness: 5.5
Density: 2.84 g/cm³
Colors: Colorless White
Streak: White
Luster: Vitreous
Transparency: Translucent
Crystal system: Monoclinic
Crystal habit: Platy Crystals, Granular Aggregates
Cleavage: Perfect
Rarity: Rare
Uses: Collector
Host rock: Metamorphosed Limestone (skarn Deposits)

Where rockhounds find killalaite

Classic worldwide localities

Killala Bay, Ireland
Fuka, Japan
Little Belt Mountains, Montana, USA

Field-hunting tip

Look in metamorphosed limestone (skarn deposits) country, the host setting where killalaite typically forms. If you start seeing calcite, cuspidine, wollastonite in float, you are in the right ground. Field specimens usually show a platy crystals, granular aggregates habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify killalaite?+

Mohs hardness is 5.5. It typically shows a vitreous luster. The streak is white. Common colors include colorless, white.

Where is killalaite found?+

Notable localities include Killala Bay, Ireland; Fuka, Japan; Little Belt Mountains, Montana, USA.

What rocks look like killalaite?+

Killalaite is most often confused with Calcite, Wollastonite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with killalaite?+

Killalaite commonly co-occurs with Calcite, Cuspidine, Wollastonite, Afwillite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does killalaite form in?+

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

What is killalaite used for?+

Killalaite is used in collector.

Find killalaite on the map

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