How to identify Ruby in Fuchsite

To correctly identify Ruby in Fuchsite (Ruby (Corundum) in Fuchsite (Muscovite variety)), 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 red (ruby) inclusions. The green can range from pale to emerald green, and the red from light pink to deep crimson.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Fuchsite exhibits a pearly to vitreous luster, while ruby can be vitreous to adamantine.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Often schistose or gneissic, with a flaky or platy appearance due to the mica. The ruby crystals are typically granular or prismatic within the matrix.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Ruby crystals are typically hexagonal prisms, often anhedral to subhedral within the fuchsite matrix. Fuchsite forms platy, micaceous crystals.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Fuchsite has perfect basal cleavage (one direction), characteristic of micas. Ruby has no cleavage but exhibits parting.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in medium to high-grade metamorphic terrains, particularly in areas where chromium-rich mafic or ultramafic rocks have undergone regional metamorphism. Often associated with greenstone belts or serpentinite bodies.

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), Pink to Red (ruby)

Luster

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

Transparency

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

Fracture

Fuchsite: Uneven; Ruby: Conchoidal to uneven

Cleavage

Fuchsite: Perfect basal (001); Ruby: None, but exhibits parting on {1011} and {0001}

Composition

Fuchsite: K(Al,Cr)2(AlSi3O10)(OH)2 (Potassium aluminum chromium silicate hydroxide); Ruby: Al2O3 (Aluminum oxide with chromium impurity)

Physical characteristics

• Crystal Habit: Fuchsite: Micaceous, platy, foliated; Ruby: Prismatic, tabular, granular, often anhedral to subhedral within the matrix.
• Cleavage Type: Fuchsite: Perfect basal; Ruby: None (parting present)
• Fracture Type: Fuchsite: Uneven; Ruby: Conchoidal to uneven
• Tenacity: Fuchsite: Flexible, elastic; Ruby: Brittle
• Luster Type: Fuchsite: Pearly to vitreous; Ruby: Vitreous to adamantine

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