How to identify Kyanite in Quartz

To correctly identify Kyanite in Quartz (Quartz with Kyanite inclusions), 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

   The quartz matrix is typically colorless, white, or gray, but can also be smoky or milky. The kyanite inclusions are most commonly blue, ranging from pale sky blue to deep indigo. They can also be white, gray, or greenish.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Quartz exhibits a vitreous (glassy) luster. Kyanite typically has a vitreous to pearly luster, especially on cleavage surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   The quartz matrix is typically massive and crystalline. The kyanite inclusions will appear as distinct bladed, columnar, or fibrous crystals embedded within the quartz.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz often forms anhedral to subhedral grains in metamorphic rocks, but can also be euhedral in vugs. Kyanite characteristically forms elongated, bladed, or columnar crystals, often with a tabular habit.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz has no true cleavage, exhibiting conchoidal fracture. Kyanite has perfect cleavage in one direction ({100}) and good cleavage in another ({010}), which can be observed on broken surfaces or within the inclusions.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   High-pressure, low-to-moderate temperature metamorphic terrains, such as those found in continental collision zones, subduction zones, and deeply buried metamorphic belts. Often associated with schists, gneisses, and eclogites.

Key Facts

Hardness

Quartz: 7 (Mohs). Kyanite: 4.5-5 parallel to length, 6-7 perpendicular to length (Mohs).

Specific Gravity

Quartz: 2.65 g/cm³. Kyanite: 3.53-3.67 g/cm³.

Crystal System

Quartz: Trigonal. Kyanite: Triclinic.

Color

Quartz: Colorless, white, gray, smoky. Kyanite: Blue, white, gray, green.

Luster

Vitreous (quartz), Vitreous to pearly (kyanite).

Transparency

Transparent to translucent (quartz), Transparent to translucent (kyanite).

Fracture

Conchoidal (quartz), Uneven to splintery (kyanite).

Cleavage

None (quartz), Perfect on {100}, good on {010} (kyanite).

Composition

Silicon dioxide (SiO2) for quartz; Aluminum silicate (Al2SiO5) for kyanite.

Physical characteristics

• Crystal Habit: Quartz: Massive, granular, prismatic. Kyanite: Bladed, columnar, fibrous, tabular.
• Cleavage Type: Quartz: None. Kyanite: Perfect in one direction, good in another.
• Fracture Type: Quartz: Conchoidal. Kyanite: Uneven to splintery.
• Tenacity: Quartz: Brittle. Kyanite: Brittle.
• Luster Type: Quartz: Vitreous. Kyanite: Vitreous to pearly.

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