How to identify Kyanite in Fuchsite

To correctly identify Kyanite in Fuchsite (Kyanite (Al2SiO5) in Fuchsite (K(Al,Cr)3Si3O10(OH)2)), 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

   Vibrant green matrix (fuchsite) with blue to bluish-white bladed crystals (kyanite). The blue of kyanite can vary in intensity.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Fuchsite exhibits a pearly to vitreous luster; kyanite is vitreous to pearly.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Typically schistose or foliated due to the mica (fuchsite) matrix. Kyanite crystals are often bladed or columnar, sometimes radiating.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Kyanite forms characteristic bladed or columnar crystals. Fuchsite forms platy, micaceous crystals.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Kyanite has perfect cleavage in one direction ({100}) and good cleavage in another ({010}), often visible as striations. Fuchsite (muscovite) has perfect basal cleavage ({001}), allowing it to split into thin sheets.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Medium to high-grade regionally metamorphosed terrains, often associated with pelitic schists, gneisses, and quartzites, particularly where chromium-bearing protoliths or metasomatism occurred.

Key Facts

Hardness

Kyanite: 4.5-5 (parallel to length), 6-7 (perpendicular to length) on Mohs scale (anisotropic hardness). Fuchsite: 2-2.5 on Mohs scale.

Specific Gravity

Kyanite: 3.53-3.67. Fuchsite: 2.77-2.88.

Crystal System

Kyanite: Triclinic. Fuchsite (Muscovite): Monoclinic.

Color

Kyanite: Blue, white, gray, green, rarely pink or black. Fuchsite: Emerald green due to chromium.

Luster

Kyanite: Vitreous to pearly. Fuchsite: Pearly to vitreous.

Transparency

Kyanite: Transparent to translucent. Fuchsite: Translucent to opaque.

Fracture

Kyanite: Uneven to splintery. Fuchsite: Uneven.

Cleavage

Kyanite: Perfect on {100}, good on {010}. Fuchsite: Perfect basal cleavage on {001}.

Composition

Kyanite: Aluminum silicate (Al2SiO5). Fuchsite: Potassium aluminum chromium silicate hydroxide (K(Al,Cr)3Si3O10(OH)2).

Physical characteristics

• Crystal Habit: Kyanite: Bladed, columnar, often radiating or intergrown. Fuchsite: Micaceous, platy, foliated aggregates.
• Cleavage Type: Kyanite: Perfect in one direction, good in another. Fuchsite: Perfect basal.
• Fracture Type: Kyanite: Uneven to splintery. Fuchsite: Uneven.
• Tenacity: Kyanite: Brittle. Fuchsite: Flexible, elastic.
• Luster Type: Kyanite: Vitreous to pearly. Fuchsite: Pearly to vitreous.

Explore Kyanite in Fuchsite