How to identify Ruby

To correctly identify Ruby (Corundum (Al2O3) variety Ruby), 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

   Ranges from pinkish-red to deep, vivid 'pigeon's blood' red. The color is due to chromium impurities.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) to adamantine.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Typically smooth on crystal faces, but can be rough in unworked specimens. Fracture is conchoidal to uneven.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Hexagonal system, typically forming tabular, prismatic, or bipyramidal crystals. Often found as barrel-shaped or tapering hexagonal prisms.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   No true cleavage, but exhibits parting along basal planes and rhombohedral planes due to lamellar twinning.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in metamorphic rocks such as marble, gneiss, and schist, and in some igneous rocks like basalt. Also commonly found in alluvial placer deposits due to its hardness and resistance to weathering.

Key Facts

Hardness

9 (Mohs scale)

Specific Gravity

3.97 - 4.05

Crystal System

Trigonal (Hexagonal system, rhombohedral division)

Color

Red, due to chromium impurities

Luster

Vitreous to adamantine

Transparency

Transparent to opaque

Fracture

Conchoidal to uneven

Cleavage

None (exhibits parting)

Composition

Aluminum oxide (Al2O3) with trace chromium (Cr)

Physical characteristics

• Crystal Habit: Typically tabular, prismatic, or bipyramidal hexagonal crystals; also granular, massive, or lamellar.
• Cleavage Type: None, but exhibits parting on {0001} (basal) and {1011} (rhombohedral) planes due to polysynthetic twinning.
• Fracture Type: Conchoidal to uneven.
• Tenacity: Brittle.
• Luster Type: Vitreous to adamantine.

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