Got a photo? Identify rocks instantly with the Rockby app
Open the appDescription
Kyanite is an aluminum silicate mineral, Al2SiO5, characterized by its distinctive anisotropic hardness (varying hardness depending on the direction of scratching). It typically forms bladed or columnar crystals, often blue, but can also be white, gray, green, or black. It is one of the three polymorphs of Al2SiO5, along with andalusite and sillimanite, each forming under different pressure-temperature conditions.
How to Identify
- Color
- Typically blue, often with color zoning (darker blue in the center, lighter blue or white on the edges). Can also be white, gray, green, or black.
- Luster
- Vitreous to pearly.
- Texture
- Bladed or columnar crystals, often intergrown. Can be massive.
- Crystal Form
- Typically forms elongated, bladed crystals, often flattened. Crystals are triclinic.
- Cleavage
- Perfect cleavage parallel to {100} and good cleavage parallel to {010}. This often results in splintery or fibrous fragments.
- Geological Environment
- Found in regionally metamorphosed pelitic rocks such as schists, gneisses, and granulites. Also occurs in some eclogites and quartz veins.
Key Facts
- Hardness: 4.5-5 parallel to length, 6-7 perpendicular to length (Mohs scale)
- Specific Gravity: 3.53-3.67
- Crystal System: Triclinic
- Color: Blue, white, gray, green, black; often color-zoned
- Luster: Vitreous to pearly
- Transparency: Transparent to translucent
- Fracture: Splintery, uneven
- Cleavage: Perfect on {100}, good on {010}
- Composition: Aluminum silicate (Al2SiO5)
Quick Check
- Color: Blue (most common), white, gray, green, black
- Luster: Vitreous to pearly
- Streak: White
Physical Characteristics
- Crystal Habit: Bladed, columnar, massive, fibrous
- Cleavage Type: Perfect in one direction ({100}), good in another ({010})
- Fracture Type: Splintery to uneven
- Tenacity: Brittle
- Luster Type: Vitreous to pearly
Formation
Kyanite is a characteristic index mineral of medium- to high-pressure regional metamorphism of pelitic (aluminum-rich) rocks. It forms from the recrystallization of clay minerals and micas under conditions of elevated pressure (typically 4-12 kbar) and moderate to high temperature (typically 400-800 C). It is commonly found in schists, gneisses, and granulites.
Usage
Kyanite is primarily used in the refractory industry due to its high melting point and resistance to thermal shock. It is used in the production of high-alumina refractories, ceramics, porcelain, and electrical insulators. Gem-quality kyanite is cut into cabochons and faceted stones for jewelry. It is also used as an abrasive.
Age Distribution
Kyanite forms under specific metamorphic conditions, so its age is tied to the age of the metamorphic events that produced it, ranging from Precambrian to Cenozoic.
Where to Find
United States
Notable occurrences in North Carolina (especially the Spruce Pine district), Georgia, Virginia, and California.
Brazil
Significant deposits, particularly for gem-quality material, in Minas Gerais.
Switzerland
Found in the Alps, often associated with high-pressure metamorphic rocks.
India
Important commercial deposits in various states, including Andhra Pradesh and Jharkhand.
Kenya
Known for some gem-quality kyanite occurrences.
Nepal
Produces fine gem-quality kyanite, particularly from the Ganesh Himal region.
Finding Tips
Look in Metamorphic Terrains
Focus your search on areas known for regional metamorphism, particularly those with pelitic schists and gneisses. Kyanite is an indicator of high-pressure metamorphic conditions.
Identify Bladed Crystals
Kyanite's characteristic bladed or columnar crystal habit is a key identifier. Look for elongated, often flattened crystals within the host rock.
Test for Anisotropic Hardness
A unique property of kyanite is its variable hardness. It is softer parallel to the length of the crystal (Mohs 4.5-5) and harder perpendicular to it (Mohs 6-7). This can be a useful diagnostic test, though it requires careful observation.
Observe Color and Cleavage
While not exclusive, the characteristic blue color and perfect cleavage (often resulting in splintery fragments) are strong indicators. Look for color zoning within crystals.
Similar Rocks
Andalusite
Andalusite
Also known as: Chiastolite (variety)
Sillimanite
Sillimanite
Also known as: Fibrolite (variety)
Blue Tourmaline
Elbaite (variety)
Also known as: Indicolite
Sapphire
Corundum
Also known as: Corundum (variety)
Scientific Classification
- Mineral Class
- Nesosilicate
- Group
- Aluminum Silicate (Al2SiO5) polymorph
- Crystal System
- Triclinic
- Chemical Formula
- Al2SiO5
- Composition
- Aluminum oxide (Al2O3) 62.9%, Silicon dioxide (SiO2) 37.1%
Explore Kyanite
Identify rocks anywhere
Free on iOS, Android, and Web. Photo identification, full database, and your personal collection.