Karlite is an extremely rare magnesium borate mineral typically found as small, prismatic, colorless to white crystals. It is best known from its type locality in Austria where it occurs within serpentinized marble contact zones.
Is this karlite?
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 karlite with a known reference. Karlite sits at Mohs 5.5, 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: silky.
- 4Match the color rangeCompare against the expected color range: light green, silky white.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: acicular, aggregates, fibrous.
Often confused with
Karlite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Danburite is the harder of the two (Mohs 7-7.25 vs. 5.5); luster reads silky on Karlite and vitreous to greasy on Danburite.
How to tell apart: Streak differs, so Karlite leaves white, Ludwigite leaves black to greenish black; luster reads silky on Karlite and submetallic on Ludwigite.
Often found alongside karlite
Minerals reported to co-occur with karlite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Mg,Al)₆.₅(BO₃)₃(OH)₄(□,Cl)₀.₅
- Mohs hardness
- 5.5
- Density
- 2.80-2.85 g/cm³
- Colors
- Light greenSilky white
- Streak
- White
- Luster
- Silky
- Transparency
- Semitransparent
- Crystal system
- Orthorhombic
- Crystal habit
- Acicular, aggregates, fibrous
- Cleavage
- Perfect on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Probably formed by Alpine metamorphism, in a calcsilicate–carbonate lens in amphibolites (Schlegeistal, Austria)
Where rockhounds find karlite
Classic worldwide localities
- Found in the Furtschaglkar, in the Schlegeistal, Zillertal, Tirol, Austria
- Cerdagne district, Pyrénées-Orientales, France
Field-hunting tip
Where it forms: Probably formed by Alpine metamorphism, in a calcsilicate–carbonate lens in amphibolites (Schlegeistal, Austria). If you start seeing calcite, dolomite, chlorite in float, you are in the right ground. Typical habit: acicular, aggregates, fibrous. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify karlite?+
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What rocks look like karlite?+
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Find karlite on the map
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