How to identify Kyanite Garnet Schist

To correctly identify Kyanite Garnet Schist (Metamorphic rock with kyanite and garnet porphyroblasts), 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

   Variable, often silvery-gray to dark gray due to mica, with distinct blue to white kyanite blades and reddish-brown to purplish-red garnet crystals.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Schistosity gives a silky to pearly luster due to mica. Kyanite can be vitreous to pearly. Garnet is typically vitreous to resinous.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Schistose (foliated) with a medium to coarse grain size. Characterized by porphyroblastic texture, where large, distinct crystals of kyanite and garnet are embedded in a finer-grained matrix.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Kyanite typically forms bladed, columnar, or tabular crystals. Garnet forms equant, dodecahedral, or trapezohedral crystals.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Kyanite exhibits perfect cleavage in one direction ({100}) and good cleavage in another ({010}). Garnet has no cleavage but exhibits conchoidal to uneven fracture. The mica matrix exhibits perfect basal cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Regional metamorphic terrains associated with convergent plate boundaries, particularly in the middle to upper amphibolite facies. Found in mountain belts and ancient shield areas.

Key Facts

Hardness

Kyanite: 4.5-5 (parallel to c-axis), 6-7 (perpendicular to c-axis). Garnet: 6.5-7.5. Mica: 2-3.

Specific Gravity

Kyanite: 3.53-3.67. Garnet: 3.5-4.3 (varies with composition).

Crystal System

Kyanite: Triclinic. Garnet: Isometric.

Color

Kyanite: Blue, white, gray, green, rarely black. Garnet: Red, reddish-brown, purplish-red, black, green, yellow, orange.

Luster

Kyanite: Vitreous to pearly. Garnet: Vitreous to resinous. Mica: Silky to pearly.

Transparency

Kyanite: Transparent to translucent. Garnet: Transparent to opaque.

Fracture

Kyanite: Splintery to uneven. Garnet: Conchoidal to uneven.

Cleavage

Kyanite: Perfect on {100}, good on {010}. Garnet: None. Mica: Perfect basal cleavage.

Composition

Predominantly aluminum silicates (kyanite, micas) and iron-magnesium aluminum silicates (garnet), with quartz and sometimes feldspar.

Physical characteristics

• Crystal Habit: Kyanite: Bladed, columnar, tabular. Garnet: Dodecahedral, trapezohedral, equant.
• Cleavage Type: Kyanite: Perfect in one direction, good in another. Garnet: None. Mica: Perfect basal.
• Fracture Type: Kyanite: Splintery to uneven. Garnet: Conchoidal to uneven.
• Tenacity: Kyanite: Brittle. Garnet: Brittle. Mica: Flexible, elastic.
• Luster Type: Vitreous, pearly, silky, resinous.

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