Kornerupine is a rare borosilicate mineral that forms elongated, prismatic crystals in high-grade metamorphic rocks. Collectors prize it for its unique color range, especially the rare blue-green hues, and its strong pleochroism which can shift from yellow-brown to green.

Hardness

6-7

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent to translucent and opaque

mineralrare

Kornerupine

Hardness: 6-7
Luster: Vitreous
Streak: White
Transparency: Transparent to translucent and opaque

Is this kornerupine?

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 kornerupine with a known reference. Kornerupine sits at Mohs 6-7, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: green, brown, colorless, greenish yellow, yellow.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: massive, prismatic.

Often confused with

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

Often found alongside kornerupine

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

All properties

Chemical formula: (Mg,Fe,Al,□)₁₀(Si,Al,B)₅O₂₁(OH,F)₂
Mohs hardness: 6-7
Density: 3.29-3.35 g/cm³
Colors: Green Brown Colorless Greenish yellow Yellow
Streak: White
Luster: Vitreous
Transparency: Transparent to translucent and opaque
Crystal system: Orthorhombic
Crystal habit: Massive, prismatic
Cleavage: Good on {110}
Rarity: Rare
Uses: Gemstone, Collector
Host rock: In boron-rich volcanic and sedimentary rocks subjected to amphibolite to granulite facies metamorphism; in metamorphosed anorthosite complexes

Where rockhounds find kornerupine

Classic worldwide localities

Fiskenæsset, Greenland
Bjordam, near Kragerö, Norway
Waldheim, Saxony, Germany
Mautia Hill, Tanzania
Bok se Puts Farm, Namaqualand, Cape Province, South Africa
Itrongahy, near Betroka, Madagascar

Field-hunting tip

Where it forms: In boron-rich volcanic and sedimentary rocks subjected to amphibolite to granulite facies metamorphism; in metamorphosed anorthosite complexes. If you start seeing sapphirine, cordierite, spinel in float, you are in the right ground. Typical habit: massive, prismatic. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify kornerupine?+

Mohs hardness is 6-7. Luster: vitreous. The streak is white. Common colors include green, brown, colorless, greenish yellow.

Where is kornerupine found?+

Notable localities include Fiskenæsset, Greenland; Bjordam, near Kragerö, Norway; Waldheim, Saxony, Germany; Mautia Hill, Tanzania; Bok se Puts Farm, Namaqualand, Cape Province, South Africa.

What rocks look like kornerupine?+

Kornerupine is most often confused with Tourmaline, Andalusite, Enstatite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with kornerupine?+

Kornerupine commonly co-occurs with Sapphirine, Cordierite, Spinel, Corundum, Tourmaline, Grandidierite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does kornerupine form in?+

Where it forms: In boron-rich volcanic and sedimentary rocks subjected to amphibolite to granulite facies metamorphism; in metamorphosed anorthosite complexes. Working float back to the host body is the standard way to chase a fresh occurrence.

What is kornerupine used for?+

Kornerupine is used in gemstone, collector.

Find kornerupine on the map

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