How to identify Sapphire (Tumbled)

To correctly identify Sapphire (Tumbled) (Corundum), 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 widely; most commonly blue, but also pink, yellow, green, purple, orange, black, and colorless. Color zoning is common. Tumbled sapphires will exhibit these natural colors.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) to adamantine (diamond-like) on polished surfaces. Tumbled sapphires will have a high, smooth, vitreous luster.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth and polished due to tumbling. Untumbled sapphire is typically granular or massive, or forms hexagonal prismatic crystals with striations.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Tumbled sapphires are anhedral (lacking well-formed crystal faces) and rounded. Original crystal forms are typically hexagonal prisms, bipyramids, or tabular forms, but these are removed by tumbling.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   No true cleavage, but exhibits parting along rhombohedral or basal planes due to lamellar twinning. This is difficult to observe in tumbled specimens.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Primary deposits in igneous rocks (e.g., basalts, syenites) and metamorphic rocks (e.g., marbles, gneisses, schists). Secondary alluvial deposits (placers) are the most common source for gem-quality material, where sapphires are concentrated due to their hardness and density. Tumbled sapphires originate from these natural occurrences.

Key Facts

Hardness

9 (Mohs scale)

Specific Gravity

3.95 - 4.03

Crystal System

Trigonal

Color

Blue, pink, yellow, green, purple, orange, black, colorless (all colors of corundum 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: Tumbled sapphires are anhedral and rounded. Untumbled: typically hexagonal prisms, bipyramids, tabular, or massive/granular.
• Cleavage Type: None, but exhibits parting on rhombohedral {101} and basal {0001} planes due to lamellar twinning.
• Fracture Type: Conchoidal to uneven
• Tenacity: Brittle
• Luster Type: Vitreous to adamantine

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