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Octagon, Octagonal | See 'Emerald Cut', and 'Radiant Cut'.
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Octahedron | A solid figure having eight sides or faces. A rough diamond with this approximate shape. The commonest crystal formation of diamond.
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Off Made, Off Make | Any diamond which does not reach good standards of cutting, particularly poor symmetry.
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Old Cut | Any cut, usually round, predating the modern brilliant cut in style.
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Old Miner | The old mine cut diamond is the earliest form of the modern brilliant cut. Also called the "cushion cut", it has a cushioned shaped girdle. This cut of diamond is characterized by a high crown, small table, deep pavilion and large culet. Other names for this cut are: old miner, Peruzzi cut, and triple cut brilliant.
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One Carat | A weight of one fifth of a gram. Any diamond of this weight.
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Open Culet | Culet which has been polished into a facet rather than being left as a point.
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Oppenheimer | Sir Ernest Oppenheimer formed Consolidated Diamond Mines about 1920, and merged them with De Beers. His son, Sir Harry Oppenheimer was later Chairman of De Beers.
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Oppenheimer Diamond Research Laboratory | Opened at Springs, on the East Rand, in 2001, together with the adjacent diamond-manufacturing plant, in the process of expanding, the largest and most advanced synthetic diamond centre in the world.
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Optic Axis | Although not relevant in diamonds, optic axis is important when distinguishing simulants.
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Orange | A rare fancy colour of diamond.
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Orlov | A large and famous diamond, which is 189.6 carats, near colourless, and rose cut.
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Orlov or Orloff Black | The Black Orlov (or Orloff) is a large famous diamond. Although not the largest black diamond, it is probably the most famous because of a supposed curse. It was originally called the Eye of Brahma, but was recut into three smaller stones.
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Oval | A fancy shape of diamond, usually a modified brilliant cut.
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There are currently over 600 entries in this table.
Over 90 of them have page links to a page on this site. Eventually, we intend to add a more complete description for most entries, each on its own page.
Please watch this space!
