How to identify Black Kyanite

To correctly identify Black Kyanite (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

   Black, often with a slightly metallic or greasy sheen due to graphite inclusions.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous to sub-vitreous, sometimes pearly on cleavage surfaces. If graphite-rich, it can appear dull to sub-metallic.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Typically bladed or columnar crystals, often forming radiating or fan-like aggregates. Can also be massive.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Triclinic system, typically forming elongated, bladed crystals. These blades can be very thin and flat.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Perfect cleavage parallel to {100} and good cleavage parallel to {010}. This results in the characteristic bladed appearance and can make it prone to splintering.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in high-pressure, low-to-moderate temperature metamorphic rocks such as schists, gneisses, and granulites, often associated with quartz, muscovite, garnet, and staurolite. The presence of carbonaceous material in the protolith is key for the black coloration.

Key Facts

Hardness

Anisotropic; 4.5-5 parallel to the long axis of the crystal, 6-7 perpendicular to the long axis (Mohs scale).

Specific Gravity

3.53-3.67 g/cm³

Crystal System

Triclinic

Color

Black (due to inclusions of graphite or other carbonaceous material, or iron oxides)

Luster

Vitreous to sub-vitreous, pearly on cleavage surfaces, sometimes dull or sub-metallic.

Transparency

Opaque to translucent (rarely).

Fracture

Splintery to uneven.

Cleavage

Perfect on {100}, good on {010}, poor on {110}.

Composition

Aluminum Silicate (Al2SiO5)

Physical characteristics

• Crystal Habit: Typically bladed, columnar, or tabular crystals, often forming radiating or fan-like aggregates. Can also be massive.
• Cleavage Type: Perfect basal cleavage on {100}, good on {010}.
• Fracture Type: Splintery to uneven.
• Tenacity: Brittle.
• Luster Type: Vitreous to sub-vitreous, pearly on cleavage surfaces.

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