How to identify Ruby

To correctly identify Ruby (Corundum (Al2O3) with Chromium impurities), 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

   Varies 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 unpolished specimens. Fracture is conchoidal.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Hexagonal system, commonly found as hexagonal prisms, tabular crystals, or bipyramidal forms. Often twinned.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None, 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

   Metamorphic rocks (marble, gneiss, schist), igneous rocks (basalt, pegmatite), and alluvial deposits.

Key Facts

Hardness

9 (Mohs scale)

Specific Gravity

3.97 - 4.05

Crystal System

Hexagonal (trigonal)

Color

Red (due to Cr3+ 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: Hexagonal prisms, tabular crystals, bipyramidal, massive, granular
• Cleavage Type: None, but exhibits parting on {0001} and {1011} due to lamellar twinning
• Fracture Type: Conchoidal to uneven
• Tenacity: Brittle
• Luster Type: Vitreous to adamantine

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