Etymology
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topaz (n.)
colored crystalline gem, late 13c., from Old French topace (11c.), from Latin topazus (source also of Spanish topacio, Italian topazio), from Greek topazos, topazion, of obscure origin. Pliny says it was named for a remote island in the Red or Arabian Sea, where it was mined, the island so named for being hard to find (from Greek topazein "to divine, to try to locate"); but this might be folk etymology, and instead the word might be from the root of Sanskrit tapas "heat, fire." In the Middle Ages used for almost any yellow stone. To the Greeks and Romans, possibly yellow olivine or yellow sapphire. In modern science, fluo-silicate of aluminum. As a color name from 1908.
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corundum (n.)

"very hard mineral" (crystalline aluminum oxide) used for grinding and polishing other gems, steel, etc., 1728, from Anglo-Indian, from Tamil (Dravidian) kurundam "ruby sapphire" (Sanskrit kuruvinda), which is of unknown origin. It is a dull or opaque variety of sapphire, amethyst, ruby, and topaz; in hardness it is next to diamond.

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