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Geosciences LibreTexts

16.12.01: Alexandrite

  • Page ID
    4339
  • Alexandrite
    Chemical composition Al2(BeO4)Beryllium aluminum oxide
    Crystal system Orthorhombic
    Habit Tabular, pseudo-hexagonal
    Cleavage Imperfect prismatic
    Fracture Weak, conchoidal
    Hardness 8.5
    Optic nature Biaxial +
    Refractive index 1.744 - 1.755
    Birefringence 0.009
    Dispersion Low, 0.014
    Specific gravity 3.70 - 3.72
    Lustre Bright vitreous
    Pleochroism Strong

    File:Alexandrite 26.75cts.jpg

    Figure \(\PageIndex{1}\): Adularescent Alexandrite 26.74 carats
    Tunduru, Ruvuma, Ruvuma Region, Tanzania

    File:Alexandrite brazil.jpg

    Figure \(\PageIndex{2}\): Alexandrite from Hematia, Minas Gerais, Brazil
    Viewed in daylight (greenish) and with LWUV (reddish)

    Figure \(\PageIndex{3}\): Alexandrite crystals photographed in candle light and daylight
    Yekaterinburg, Russia

    Alexandrite is a phenomenal variety of the mineral chrysoberyl. Because of the trace amounts of the chromophores vanadium and chromium, alexandrite appears different colors depending on whether it is viewed in natural or incandescent light. In daylight, the stone appears to be green; in artificial light it appears to be raspberry red. It was originally discovered in the Ural Mountains in 1830 on the birthday of Czar Alexander of Russia. Another extraordinary coincidence was that the national colors of Russia were red and green. Today, alexandrite is found in Russia, Brazil, India and to a lesser extent in Africa. Alexandrite has long been associated with great luck and prosperity.

    Inclusion Images

    Figure \(\PageIndex{4}\): Liquid veil and twinning resembling a venetian blind effect
    Courtesy of Barbra Voltaire

    Additional Phenomena

    Alexandrite image gallery

    • Cat's Eye

    File:Alex-blue.gif

    Figure \(\PageIndex{5}\): Cat's eye Alexandrite under daylight
    Photo courtesy of The Gem Trader

    File:Alex-purple.gif

    Figure \(\PageIndex{6}\): Cat's eye Alexandrite under incandescent light; Photo courtesy of The Gem Trader