Larnite is a rare calcium silicate mineral primarily found in high-temperature contact metamorphic environments, such as limestone altered by magma or coal seam combustion. It typically appears as nondescript, colorless to gray masses and is challenging for amateur collectors to identify without professional lab analysis. It is most famous as a synthetic constituent of Portland cement clinker.
Is this larnite?
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 larnite with a known reference. Larnite sits at Mohs 6, 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, gray.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: granular, tabular.
Often confused with
Larnite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside larnite
Minerals reported to co-occur with larnite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₂SiO₄
- Mohs hardness
- 6
- Density
- 3.28-3.33 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Granular, tabular
- Cleavage
- {100}, good; {010}, imperfect
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- In contact metamorphic terranes involving sedimentary carbonate rocks
Where rockhounds find larnite
Classic worldwide localities
- Marble Canyon, Culberson Co., Texas, USA
- Scawt Hill and Ballycraigy, near Larne, Co. Antrim, Ireland
- Bellerberg volcano, two km north of Mayen, Eifel district, Germany
- Hatrurim Formation, Israel
- Rehia, and in Golden Gully, Tokatoka district, about 150 km north of Auckland, New Zealand
- Gosse Pile, Tomkinson Ranges, and in the Deering Hills, South Australia
Field-hunting tip
Where it forms: In contact metamorphic terranes involving sedimentary carbonate rocks. If you start seeing spurrite, melilite, gehlenite in float, you are in the right ground. Typical habit: granular, tabular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify larnite?+
Where is larnite found?+
What rocks look like larnite?+
What minerals are found with larnite?+
What kind of rock does larnite form in?+
What is larnite used for?+
Find larnite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
