Geuda
Encyclopedia
Geuda is a form of the mineral corundum
, or sapphire
, found primarily in Sri Lanka
. Around 70%-80% gems mined in Sri Lanka belongs to Geuda varieties. Because of its semitransparent and milky appearance due to TiO2 (Rutile), 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 1970s discovery that heat treatment can drastically alter the stone's color. Ottu,Dun,Diesel,Milky,silky are some Geuda varieties which give blue colour after heat treatments.Deguna and Red Geuda turn to red after oxidizing.Kowangu pushparaga ( pronounced koo-wangu )turns to yellow sapphire after oxidizing. 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.
Corundum
Corundum is a crystalline form of aluminium oxide with traces of iron, titanium and chromium. It is a rock-forming mineral. It is one of the naturally clear transparent materials, but can have different colors when impurities are present. Transparent specimens are used as gems, called ruby if red...
, or sapphire
Sapphire
Sapphire is a gemstone variety of the mineral corundum, an aluminium oxide , when it is a color other than red or dark pink; in which case the gem would instead be called a ruby, considered to be a different gemstone. Trace amounts of other elements such as iron, titanium, or chromium can give...
, found primarily in Sri Lanka
Sri Lanka
Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka is a country off the southern coast of the Indian subcontinent. Known until 1972 as Ceylon , Sri Lanka is an island surrounded by the Indian Ocean, the Gulf of Mannar and the Palk Strait, and lies in the vicinity of India and the...
. Around 70%-80% gems mined in Sri Lanka belongs to Geuda varieties. Because of its semitransparent and milky appearance due to TiO2 (Rutile), 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 1970s discovery that heat treatment can drastically alter the stone's color. Ottu,Dun,Diesel,Milky,silky are some Geuda varieties which give blue colour after heat treatments.Deguna and Red Geuda turn to red after oxidizing.Kowangu pushparaga ( pronounced koo-wangu )turns to yellow sapphire after oxidizing. 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.