D is the abbreviation of diamond, which means diamond, and ct is carat, which is the abbreviation of carat, the weight unit of diamond.
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The color grade of diamonds from high to low is D E F G H I J K L M N, and from white to yellow, relatively speaking, D has higher grade and better color.
Color grading of diamonds. Diamonds can be divided into four color series: colorless transparent to light yellow series, brown to brown series, gray series and color series.
Most jewelry diamonds belong to colorless transparent to light yellow series, and only this series of diamonds has established clear color grades, grading rules and corresponding standard samples. China's national standards for jewelry and jade classify colorless transparent to light yellow (including brown and gray) diamonds into twelve grades.