How to identify Sapphire

To correctly identify Sapphire (Corundum (Al₂O₃)), 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

   Typically blue, but can be yellow, pink, orange, green, purple, black, or colorless (white sapphire). The color is often unevenly distributed, appearing as bands or zones.

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

   Smooth to slightly rough on crystal faces; often exhibits growth striations.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Hexagonal system, commonly forming barrel-shaped, bipyramidal, tabular, or prismatic crystals. Often found as rounded pebbles in alluvial deposits.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   No true cleavage, but exhibits parting along basal planes ({0001}) and rhombohedral planes ({1011}) due to lamellar twinning. This parting can resemble cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Primary deposits are found in metamorphic rocks (e.g., gneisses, schists, marbles), silica-undersaturated igneous rocks (e.g., alkali basalts, nepheline syenites, lamprophyres), and desilicated pegmatites. Secondary (placer) deposits are found in alluvial gravels and riverbeds, where sapphires have been eroded from their primary sources and concentrated due to their high density and hardness.

Key Facts

Hardness

9 (Mohs scale)

Specific Gravity

3.95 - 4.10 g/cm³

Crystal System

Trigonal

Color

Blue, yellow, pink, green, orange, purple, black, colorless (all colors except red)

Luster

Vitreous to adamantine

Transparency

Transparent to opaque

Fracture

Conchoidal to uneven

Cleavage

None (exhibits parting)

Composition

Aluminum oxide (Al₂O₃)

Physical characteristics

• Crystal Habit: Typically hexagonal prisms, often barrel-shaped, bipyramidal, or tabular. Can be massive or granular.
• Cleavage Type: None, but exhibits parting on {0001} (basal) and {1011} (rhombohedral) planes due to polysynthetic twinning.
• Fracture Type: Conchoidal to uneven, brittle.
• Tenacity: Brittle
• Luster Type: Vitreous to adamantine

Explore Sapphire