How to identify Ruby in Fuchsite

To correctly identify Ruby in Fuchsite (Corundum in Fuchsite (Chromian Muscovite)), 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

   Dominantly green (fuchsite) with distinct red (ruby) inclusions. The green can range from pale to deep emerald green, often with a silvery sheen. The red rubies are typically opaque and can vary from pinkish-red to deep crimson.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Fuchsite exhibits a pearly to vitreous luster, often with a shimmering or metallic sheen due to its micaceous nature. Ruby inclusions are typically dull to sub-adamantine.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Schistose texture, meaning it has a foliated or layered appearance due to the alignment of mica flakes. The ruby crystals are often granular or blocky, embedded within the micaceous matrix.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Fuchsite occurs as small, platy, hexagonal crystals, often intergrown to form a micaceous mass. Ruby (corundum) typically forms hexagonal prisms or barrel-shaped crystals, often anhedral (lacking well-formed faces) within the matrix.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Fuchsite (muscovite) has perfect basal cleavage in one direction, allowing it to split into thin, flexible sheets. Ruby (corundum) has no true cleavage but exhibits parting along rhombohedral planes.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in regionally metamorphosed terrains, particularly in areas where ultramafic rocks (e.g., serpentinites, peridotites) or chromium-rich sediments have undergone medium to high-grade metamorphism. It is often associated with greenstone belts and ancient cratons.

Key Facts

Hardness

Fuchsite: 2.5-3 (Mohs); Ruby: 9 (Mohs)

Specific Gravity

Fuchsite: 2.77-2.88; Ruby: 3.97-4.05

Crystal System

Fuchsite: Monoclinic; Ruby: Trigonal

Color

Green (fuchsite), Red (ruby)

Luster

Pearly to vitreous (fuchsite), Dull to sub-adamantine (ruby)

Transparency

Fuchsite: Translucent to opaque; Ruby: Opaque (in this context)

Fracture

Fuchsite: Uneven to splintery; Ruby: Conchoidal to uneven

Cleavage

Fuchsite: Perfect basal cleavage (001); Ruby: No true cleavage, but parting on {1011} and {0001}

Composition

Fuchsite: K(Al,Cr)2(AlSi3O10)(OH)2; Ruby: Al2O3 (with Cr3+ impurities)

Physical characteristics

• Crystal Habit: Fuchsite: Micaceous, platy, foliated; Ruby: Granular, anhedral to subhedral hexagonal prisms
• Cleavage Type: Fuchsite: Perfect basal; Ruby: Parting
• Fracture Type: Fuchsite: Uneven to splintery; Ruby: Conchoidal to uneven
• Tenacity: Fuchsite: Flexible, elastic; Ruby: Brittle
• Luster Type: Fuchsite: Pearly to vitreous; Ruby: Dull to sub-adamantine

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