How to identify Kyanite

To correctly identify Kyanite (Al2SiO5), check each of these features in order. Many rocks and minerals look alike, so cross-reference multiple properties before deciding.

Step-by-step identification

1. 1

   Color

   Overall color and any zoning or banding

   Typically blue, often with color zoning (darker blue in the center, lighter at the edges). Can also be white, gray, green, or black.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous to pearly.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Bladed or columnar crystals, often intergrown or radiating. Can be massive.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Triclinic system, typically forming elongated, bladed, or columnar crystals. Crystals are often flattened parallel to {100}.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Perfect cleavage parallel to {100}, good cleavage parallel to {010}. This often results in splintery or fibrous fragments.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Metamorphic rocks, particularly schists, gneisses, and granulites derived from aluminum-rich sedimentary rocks (pelites). Also found in some eclogites and quartz veins.

Key Facts

Hardness

4.5-5.5 (perpendicular to length) to 7 (parallel to length) on the Mohs scale (anisotropic hardness)

Specific Gravity

3.53-3.67 g/cm³

Crystal System

Triclinic

Color

Blue, white, gray, green, black

Luster

Vitreous to pearly

Transparency

Transparent to translucent

Fracture

Splintery to uneven

Cleavage

Perfect on {100}, good on {010}

Composition

Aluminum Silicate (Al2SiO5)

Physical characteristics

• Crystal Habit: Typically bladed, columnar, or tabular crystals; also massive, radiating, or fibrous aggregates.
• Cleavage Type: Perfect basal cleavage on {100}, good cleavage on {010}. This often results in step-like or splintery fractures.
• Fracture Type: Splintery to uneven, due to its excellent cleavage.
• Tenacity: Brittle
• Luster Type: Vitreous on crystal faces, pearly on cleavage surfaces.

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