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 6 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Karlite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Karlite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white, gray.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: prismatic crystals.
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 7-7.5 vs. 6).
How to tell apart: Karlite is noticeably harder (Mohs 6 vs. 5); streak differs — Karlite leaves white, Ludwigite leaves black; luster reads vitreous 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
- Mg₁₁B₇O₁₈(OH,Cl)₁₀
- Mohs hardness
- 6
- Density
- 3.37 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Prismatic Crystals
- Cleavage
- Distinct On {110}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Serpentinized Marble
- Typical price
- $50-300 per specimen
Where rockhounds find karlite
Classic worldwide localities
- Karlstift, Austria
Field-hunting tip
Look in serpentinized marble country — that is the host setting where karlite typically forms. If you start seeing ludwigite, magnetite, serpentine in float, you are in the right ground. Field specimens usually show a prismatic crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find karlite on the map
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