How to identify Ruby in Fuchsite

To correctly identify Ruby in Fuchsite (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 red to pinkish-red inclusions (ruby). May also have minor black specks (hornblende or other dark minerals).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Fuchsite matrix exhibits a pearly to vitreous luster, often shimmering due to its micaceous nature. Ruby inclusions are typically sub-adamantine to vitreous.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Schistose texture due to the alignment of mica flakes. The ruby crystals are typically granular or blocky within the micaceous matrix.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Ruby crystals are typically anhedral to subhedral, often appearing as rounded or irregular masses within the fuchsite. Fuchsite forms platy, flaky crystals.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Fuchsite exhibits perfect basal cleavage (one direction). Ruby has no true cleavage but exhibits parting along rhombohedral planes.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

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

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 to pinkish-red (ruby)

Luster

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

Transparency

Fuchsite: Translucent to opaque; Ruby: Opaque to translucent

Fracture

Fuchsite: Uneven; Ruby: Conchoidal to uneven

Cleavage

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

Composition

Fuchsite: K(Al,Cr)2(AlSi3O10)(OH)2 (Chromium-rich Muscovite); Ruby: Al2O3 (Chromium-rich Corundum)

Physical characteristics

• Crystal Habit: Fuchsite: Platy, flaky, micaceous aggregates; Ruby: Granular, massive, anhedral to subhedral crystals within the matrix.
• Cleavage Type: Fuchsite: Perfect in one direction (basal); Ruby: No true cleavage, but exhibits parting.
• Fracture Type: Fuchsite: Uneven; Ruby: Conchoidal to uneven.
• Tenacity: Fuchsite: Flexible, elastic; Ruby: Brittle.
• Luster Type: Fuchsite: Pearly to vitreous; Ruby: Sub-adamantine to vitreous.

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