Alexandrite

Alexandrite
Alexandrite is the color-change variety of chrysoberyl. The most distinctive specimens appear to have a green to blue-green color in daylight but change to a red to purplish-red color under incandescent light. Specimens with strong and distinct color-change properties are rare, highly desirable, and sell at very high prices. Stones over five carats are especially rare. A photo pair of an alexandrite gem in daylight and incandescent light is shown on this page.

The change in color is thought to occur only in specimens where chromium substitutes for aluminum in the mineral's atomic structure. The chrysoberyl in which this phenomenon was first observed was named "alexandrite" after Tsar Alexander II of Russia. Since then the "alexandrite effect" has been observed in other gems, which include color-change garnet, spinel, tourmaline, sapphire, and fluorite. This table was created by Geology.com! {| class="wikitable"
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Physical Properties of Chrysoberyl

 * Chemical Classification
 * Oxide
 * Color
 * Usually ranges from brown to pale yellow, yellow-green and green
 * Streak
 * Colorless
 * Luster
 * Vitreous
 * Diaphaneity
 * Transparent to translucent
 * Cleavage
 * Poor, prismatic
 * Mohs Hardness
 * 8.5
 * Specific Gravity
 * 3.7 to 3.8
 * Diagnostic Properties
 * Hardness, color
 * Chemical Composition
 * Beryllium aluminum oxide, BeAl2O4
 * Crystal System
 * Orthorhombic
 * Uses
 * As a gemstone: chrysoberyl when transparent, "cat's-eye" when chatoyant, and "alexandrite" in specimens that exhibit color change.
 * }
 * Diagnostic Properties
 * Hardness, color
 * Chemical Composition
 * Beryllium aluminum oxide, BeAl2O4
 * Crystal System
 * Orthorhombic
 * Uses
 * As a gemstone: chrysoberyl when transparent, "cat's-eye" when chatoyant, and "alexandrite" in specimens that exhibit color change.
 * }
 * Uses
 * As a gemstone: chrysoberyl when transparent, "cat's-eye" when chatoyant, and "alexandrite" in specimens that exhibit color change.
 * }