Kornerupine Mineral Overview
- Mineral name: Kornerupine
- Mineral class: Silicate (borosilicate)
- Chemical formula: (Mg,Fe)₃Al₆(Si,Al,B)₅O₂₁(OH) (variable)
- Crystal system: Orthorhombic
- Mohs hardness: 6.5–7
- Color range: Green, brown, yellow, colorless, bluish-green
- Luster: Vitreous
- Streak: White
- Cleavage: Poor
- Fracture: Uneven to conchoidal
- Specific gravity: Approximately 3.2–3.4
- Transparency: Transparent to translucent
- Common locations: Greenland, Sri Lanka, Madagascar, Tanzania
- Uses: Gemstone, collector mineral
- Similar minerals: Andalusite, sillimanite, tourmaline
Naming and Classification
Kornerupine is a boron-bearing silicate mineral, named after Danish geologist Andreas Nikolaus Kornerup.
It is classified as a borosilicate, meaning it contains:
- Silicon (Si)
- Boron (B)
This places it among a relatively small group of minerals that incorporate boron into their crystal structure.
Physical and Optical Characteristics
Kornerupine typically occurs as:
- Prismatic to elongated crystals
- Massive or granular aggregates
Its color varies widely, but common shades include:
- Olive green
- Brownish-green
- Yellow or honey tones
- Rare bluish-green
The luster is vitreous, giving it a glassy appearance.
With a Mohs hardness of 6.5–7, it is relatively durable.
Pleochroism (Key Feature)
Kornerupine is known for:
- Strong pleochroism
This means it can show different colors when viewed from different angles, such as:
- Green → brown → yellow
This optical effect is important for identifying and evaluating gem-quality specimens.
Chemical Composition and Structure
Kornerupine is composed of:
- Magnesium (Mg) and iron (Fe)
- Aluminum (Al)
- Silicon (Si)
- Boron (B)
- Hydroxyl (OH)
It has a complex silicate framework, with boron incorporated into the structure, which is relatively uncommon.
Formation and Geological Occurrence
Kornerupine forms in high-grade metamorphic environments, particularly:
Aluminum-Rich Metamorphic Rocks
- Gneiss
- Schist
Boron-Rich Conditions
- Presence of boron-bearing fluids
Typical formation conditions include:
- High temperatures and pressures
- Metamorphism of aluminum-rich sediments
It is commonly associated with:
- Sillimanite
- Garnet
- Spinel
Common Locations
Kornerupine is found in several notable regions:
- Greenland: Type locality
- Sri Lanka: Gem gravels
- Madagascar: Important gem source
- Tanzania: Additional occurrences
Sri Lanka and Madagascar are known for gem-quality material.
Uses and Practical Significance
Kornerupine is valued for:
Gemstone Use
- Faceted into gemstones
- Appreciated for pleochroism and rarity
Collector Mineral
- Interesting crystal habit and composition
It has no major industrial use.
Similar and Related Minerals
Kornerupine can resemble:
- Andalusite: Also pleochroic but different chemistry
- Sillimanite: Similar environment but different structure
- Tourmaline: More common and typically more colorful
Optical properties and chemical composition help distinguish it.
Identification Notes for Collectors
- Look for green to brown prismatic crystals
- Note moderate hardness (6.5–7)
- Observe strong pleochroism under light
- Check vitreous luster
- Consider occurrence in high-grade metamorphic rocks
Kornerupine is a boron-bearing silicate mineral, recognized for its pleochroism and occurrence in high-grade metamorphic environments, making it a rare and attractive gemstone and collector specimen.