How to identify Ruby in Fuchsite

To correctly identify Ruby in Fuchsite (Corundum (Ruby) 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 pink to deep red (ruby) inclusions. White or grey areas may indicate other minerals like quartz or feldspar.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Fuchsite exhibits a pearly to vitreous luster, while ruby is typically vitreous to adamantine. The overall rock can appear somewhat shimmery due to the mica.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Often schistose or foliated, reflecting the alignment of mica flakes. Ruby crystals are typically anhedral to subhedral, appearing as opaque masses or hexagonal prisms within the matrix.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Ruby crystals are usually massive, granular, or anhedral to subhedral hexagonal prisms. Fuchsite forms platy, micaceous crystals.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

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

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in regionally metamorphosed chromium-rich ultramafic rocks, often associated with greenstone belts or ancient cratons.

Key Facts

Hardness

Ruby: 9 (Mohs); Fuchsite: 2.5-3 (Mohs). The overall rock will have variable hardness.

Specific Gravity

Ruby: 3.95-4.10; Fuchsite: 2.77-2.88. The rock's specific gravity will be an average of its components.

Crystal System

Ruby (Corundum): Trigonal; Fuchsite (Muscovite): Monoclinic

Color

Green (fuchsite) and pink to deep red (ruby)

Luster

Pearly to vitreous (fuchsite), vitreous to adamantine (ruby)

Transparency

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

Fracture

Ruby: Conchoidal to uneven; Fuchsite: Uneven

Cleavage

Ruby: None (parting present); Fuchsite: Perfect basal cleavage (one direction)

Composition

Ruby: Aluminum oxide (Al2O3) with chromium impurities; Fuchsite: Hydrous potassium aluminum silicate (K(Al,Cr)2(AlSi3O10)(OH)2) with chromium substituting for some aluminum.

Physical characteristics

• Crystal Habit: Ruby: Massive, granular, anhedral to subhedral hexagonal prisms; Fuchsite: Micaceous, platy, foliated aggregates.
• Cleavage Type: Fuchsite: Perfect basal cleavage {001}; Ruby: No true cleavage, but exhibits parting on {1011} and {0001}.
• Fracture Type: Ruby: Conchoidal to uneven; Fuchsite: Uneven.
• Tenacity: Ruby: Brittle; Fuchsite: Flexible, elastic.
• Luster Type: Fuchsite: Pearly to vitreous; Ruby: Vitreous to adamantine.

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