How to identify Alexandrite

To correctly identify Alexandrite (Chrysoberyl variety), 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

   Emerald green to bluish-green in daylight/fluorescent light; raspberry red to purplish-red in incandescent light. The strength of the color change is a key identifier.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) to sub-adamantine.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth, often with striations on crystal faces.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Orthorhombic, typically forming tabular or prismatic crystals, often twinned, particularly as pseudohexagonal trillings (three crystals intergrown at 120 degrees).

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Distinct on {110}, but rarely observed in gem material due to its toughness.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in pegmatites, mica schists, and contact metamorphic deposits. Also occurs in alluvial deposits derived from these primary sources.

Key Facts

Hardness

8.5 (Mohs scale)

Specific Gravity

3.70-3.78

Crystal System

Orthorhombic

Color

Green to bluish-green (daylight/fluorescent); Red to purplish-red (incandescent)

Luster

Vitreous to sub-adamantine

Transparency

Transparent to translucent

Fracture

Conchoidal to uneven

Cleavage

Distinct on {110}, but rarely observed

Composition

Beryllium aluminum oxide with chromium impurities (BeAl2O4:Cr)

Physical characteristics

• Crystal Habit: Tabular, prismatic, often twinned (pseudohexagonal trillings)
• Cleavage Type: Distinct on {110}, but typically not seen in gem material due to toughness
• Fracture Type: Conchoidal to uneven
• Tenacity: Brittle
• Luster Type: Vitreous to sub-adamantine

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