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cat's eye
The mineral or gemstone chrysoberyl is an aluminate of berylliumwith the formula BeAl2O4. THe word comes from the Greek words for gold and beryl.
Ex.: emerald, mallachite, chrysoberyl
Emerald, Malachite, and Chrysoberyl etc
Reference: What_minerals_are_used_to_make_a_bright_green_color_or_special_effect
Alexandrite is the "scientific name" of the mineral.
Alexandrite is a type of chrysoberyl (formula BeAl2O4), which may be what you were asking. Alexandrite is specifically chrysoberyl with some of the aluminium atoms replaced with chromium.