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The carat (ct) is a unit of mass equal to 200 mg (0.00705 oz; 0.00643 ozt), which is used for measuring gemstones and pearls. The current definition, sometimes known as the metric carat , was adopted in 1907 at the Fourth General Conference on Weights and Measures , [ 1 ] [ 2 ] and soon afterwards in many countries around the world.
This is a partial list of the largest non-synthetic diamonds with a rough stone (uncut) weight of over 200 carats (40 grams). [1] The list is not intended to be complete—e.g., the Cullinan (formerly Premier) mine alone has produced 135 diamonds larger than 200 carats since mining commenced.
A 5.05-carat (1.010 g) Emerald-cut red diamond formerly known simply as "Red Diamond". This is the second-largest known red diamond. It was cut from a 35-carat (7.0 g) piece of boart discovered near Lichtenburg, South Africa. It reappeared in 2007 after a 37-year absence from sight, and was purchased by Kazanjian Brothers Inc. —
These stones (such as EightStar-brand diamonds) have less light leakage at the edge of the stone (for a given crown angle, pavilion angle, and table ratio). Some diamonds with painted girdles receive lower grades in the GIA's cut grading system, for reasons given in a 2005 GIA article. [11] Several groups have developed diamond cut grading ...
Diamond reports from GIA (as well as other, for-profit sources) are now demanded by most consumers purchasing diamonds over a certain size, typically for over 0.5 carat (100 mg), and almost always for over 1.0 carat (200 mg), and are considered an important tool in guaranteeing that a diamond is accurately represented to a potential buyer.
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According to Graff, the stone is the "largest highest clarity, highest color diamond ever graded by the Gemological Institute of America (GIA)". The other 66 stones cut from the original Lesedi La Rona range in size from 26 carats (5.2 g; 0.18 oz) to below one carat (0.20 g; 0.0071 oz).
The Centenary Diamond is rated in color as grade D color by the Gemological Institute of America, which is the highest grade of colourless diamond and is internally and externally flawless. It was named the Centenary Diamond as it was presented in the rough for the Centennial Celebration of De Beers Consolidated Mines on 11 May 1988.