# How to identify kyanite

Canonical page: https://lithomap.app/resources/mineral-identification/kyanite
Last reviewed: September 17, 2026
Page purpose: Original LithoMap mineral identification reference for field observations, search systems, and language models.
Classification: Aluminum silicate · Al₂SiO₅

## Summary

Kyanite is a bladed aluminum silicate mineral with strongly directional hardness, commonly blue to gray, that forms in aluminum-rich metamorphic rocks at elevated pressure.

## Quick identification clues

- Long bladed or tabular crystals
- Hardness differs strongly by direction
- Commonly blue, gray, white, or green
- Perfect cleavage parallel to the blade length

## Composition and classification

Kyanite is Al₂SiO₅, the same chemical composition as andalusite and sillimanite but with a different crystal structure stable under different pressure-temperature conditions.

## Appearance

Crystals are typically elongated, flattened blades with parallel striations and vitreous to pearly luster. Blue color may be patchy or concentrated along the crystal center.

Kyanite also occurs gray, white, green, blackish, or colorless and may form radiating aggregates or embedded blades in schist, gneiss, and quartz-rich rock.

## Identification tests

- Directional hardness: About 4.5 to 5 parallel to length and 6.5 to 7 across the blade. The unusual hardness anisotropy is a major clue on expendable material.
- Cleavage: Perfect in one direction and good in another. Blades split along flat surfaces and may be brittle.
- Habit: Elongated flattened blades. Separates it from equant corundum and many blue minerals.
- Streak: White. Expected but not diagnostic.

## Common lookalikes

- Corundum: Uniformly much harder at Mohs 9 and lacks kyanite’s bladed cleavage habit.
- Blue tourmaline: Harder and commonly forms deeply striated trigonal prisms with poor cleavage.
- Sillimanite: Commonly fibrous or slender-prismatic and does not show the same extreme directional hardness.

## Direct side-by-side comparisons

- Kyanite vs. corundum — https://lithomap.app/resources/mineral-identification/compare/kyanite-vs-corundum

## Most relevant related guides

- Corundum — https://lithomap.app/resources/mineral-identification/corundum
- Tourmaline — https://lithomap.app/resources/mineral-identification/tourmaline
- Apatite — https://lithomap.app/resources/mineral-identification/apatite
- Augite — https://lithomap.app/resources/mineral-identification/augite

## Formation

Kyanite forms during medium- to high-grade metamorphism of aluminum-rich sedimentary rocks, especially under relatively high pressure.

Its presence helps constrain metamorphic conditions when mineral assemblage and regional context are evaluated together.

## Occurrence and geologic setting

Kyanite occurs in metamorphic belts, commonly in mica schist, gneiss, quartzite, and high-pressure metamorphic rocks.

Color alone cannot establish kyanite, and directional hardness should not be tested on valuable crystals.

## Uses and significance

Kyanite and related aluminum silicates are used in heat-resistant refractories, ceramics, kiln furniture, foundry products, and other high-temperature applications.

## Field safety and limitations

- Test hardness in two directions only on expendable material.
- Bladed crystals can split and form sharp edges.
- Do not infer metamorphic pressure from one loose specimen without field context.

## Authoritative sources

- Kyanite and Related Minerals Statistics and Information — U.S. Geological Survey: https://www.usgs.gov/centers/national-minerals-information-center/kyanite-and-related-minerals-statistics-and-information
- Minerals and their physical properties — U.S. National Park Service: https://www.nps.gov/subjects/geology/minerals.htm
- Mohs Hardness Scale — U.S. National Park Service: https://www.nps.gov/articles/mohs-hardness-scale.htm
- Natural Gemstones: Mineral Gemstones — U.S. Geological Survey: https://pubs.usgs.gov/gip/gemstones/mineral.html

## Specimen photograph

- Image: https://lithomap.app/_delivery/identification/minerals/kyanite.webp
- Description: Intergrown bladed kyanite crystals about five centimeters across from Boehl’s Butte, Idaho
- Creator: Shannon Heinle
- License: CC0 1.0 — https://creativecommons.org/publicdomain/zero/1.0/
- Source record: https://commons.wikimedia.org/wiki/File:Kyanite_%28GeoDIL_number_-_386%29.jpg

This reference supports preliminary field identification. It is not a laboratory determination, appraisal, hazard assessment, proof of origin, or statement of land ownership, legal access, or collecting permission.