How to identify Ruby

To correctly identify Ruby (Corundum (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 a deep, vivid 'pigeon's blood' red. The color is often unevenly distributed, appearing as streaks or spots.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) to adamantine (diamond-like) on crystal faces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Typically smooth on crystal faces, but can be rough or etched in natural occurrences.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Hexagonal system, commonly 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

   None (parting may be observed along twinning planes or basal planes, but this is not true cleavage).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Metamorphic rocks (marbles, gneisses, schists), silica-undersaturated igneous rocks (basalts, syenites), and alluvial deposits derived from these primary sources.

Key Facts

Hardness

9 (Mohs scale)

Specific Gravity

3.97 - 4.05

Crystal System

Hexagonal (Trigonal)

Color

Red, pinkish-red, purplish-red, brownish-red

Luster

Vitreous to adamantine

Transparency

Transparent to opaque

Fracture

Conchoidal to uneven

Cleavage

None (parting sometimes observed)

Composition

Aluminum Oxide (Al2O3) with trace Chromium (Cr)

Physical characteristics

• Crystal Habit: Tabular, prismatic, bipyramidal, barrel-shaped, massive, granular
• Cleavage Type: None (parting on {0001} and {1011} due to twinning)
• Fracture Type: Conchoidal to uneven
• Tenacity: Brittle
• Luster Type: Vitreous to adamantine

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