Geuda

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Geuda (pronounced gay-oo-dah) is a form of the mineral corundum, or sapphire, found primarily in Sri Lanka. Because of its semitransparent and milky appearance, these stones have little value as gemstones in their natural state.

Geuda was frequently stored in large drums or used to gravel home gardens prior to the 1970's discovery that heat treatment can drastically alter the stone's color.^[1] After heating geuda to roughly 1800 degrees Celsius, the aluminum oxide lattice-work of the gem is disrupted and cooling greatly improves both color and clarity. Though many stones are destroyed by the heating and cooling process, those that survive are significantly altered and rival naturally blue sapphires in both appearance and price.

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