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 typically unevenly distributed, often concentrated in patches or streaks.

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 to the touch, with a dense, compact feel.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Hexagonal system, commonly found as tabular, prismatic, or bipyramidal crystals. Often twinned.

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 (marbles, gneisses, schists), igneous rocks (basalts, syenites), and secondary alluvial deposits derived from these primary sources.

Key Facts

Hardness

9 on the Mohs scale

Specific Gravity

3.97 - 4.05

Crystal System

Hexagonal (trigonal)

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 prismatic, tabular, or bipyramidal crystals; also granular, massive, or in lamellar aggregates. Often twinned.
• Cleavage Type: No true cleavage; exhibits parting along basal planes {0001} and rhombohedral planes {1011} due to lamellar twinning.
• Fracture Type: Conchoidal to uneven, brittle.
• Tenacity: Brittle
• Luster Type: Vitreous to adamantine

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