How to identify Yellow Sapphire

To correctly identify Yellow 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

   Ranges from pale lemon yellow to intense canary yellow, golden yellow, or even orange-yellow. The color is typically uniform but can show slight zoning.

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, conchoidal fracture surfaces.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Hexagonal system, commonly found as barrel-shaped, bipyramidal, or tabular crystals. Often found as water-worn 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 and rhombohedral planes due to lamellar twinning.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in primary deposits within metamorphic rocks (e.g., marble, gneiss, schist) and certain igneous rocks (e.g., syenites, desilicated pegmatites). More commonly found in secondary alluvial or eluvial placer deposits, where they have been weathered out of their primary host rocks and concentrated by water action.

Key Facts

Hardness

9 (Mohs scale)

Specific Gravity

3.95-4.10

Crystal System

Trigonal (often described as Hexagonal for practical purposes)

Color

Yellow, golden yellow, orange-yellow

Luster

Vitreous to adamantine

Transparency

Transparent to translucent

Fracture

Conchoidal to uneven

Cleavage

None (exhibits parting)

Composition

Aluminum oxide (Al2O3) with trace impurities of iron (Fe3+) and sometimes titanium (Ti4+) causing the yellow color.

Physical characteristics

• Crystal Habit: Typically prismatic, tabular, bipyramidal, or barrel-shaped crystals. Often found as rounded pebbles in alluvial deposits.
• Cleavage Type: No true cleavage, but exhibits parting along the basal pinacoid {0001} and rhombohedral planes {1011} due to polysynthetic twinning.
• Fracture Type: Conchoidal to uneven, brittle.
• Tenacity: Brittle
• Luster Type: Vitreous (glassy) to adamantine (diamond-like)

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