How to identify Ruby

To correctly identify Ruby (Corundum (Al 2O 3)), 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 blood-red. The most valuable rubies are a pure, saturated red with a slight purplish secondary hue.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous to adamantine.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth to slightly rough on crystal faces; conchoidal fracture surfaces are smooth and glassy.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Typically forms as hexagonal prisms, often with flat basal pinacoids or bipyramidal terminations. Can also be found as granular or massive aggregates.

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. This parting is not as clean or easy as true cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in metamorphic rocks (marbles, gneisses, schists), igneous rocks (basalts, syenites), and alluvial placer deposits derived from these primary sources.

Key Facts

Hardness

9 (Mohs scale)

Specific Gravity

3.97 - 4.05

Crystal System

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

Physical characteristics

• Crystal Habit: Prismatic, tabular, bipyramidal, granular, massive
• Cleavage Type: None (parting on {0001} and {1011})
• Fracture Type: Conchoidal to uneven
• Tenacity: Brittle
• Luster Type: Vitreous to adamantine

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