Lesson 2: Carats and Gemstone Grading

Step 4: Gem Grading

Lesson 2

What are Carats?

Carat is one of the four Cs of gemstone grading. In English, that sounds the same as carrot, but we aren’t discussing vegetables. Carat also sounds the same as karat, but that is a measure of the fineness of gold or the ratio of pure gold to alloy metals in a mixture. Karat is abbreviated as “K.”

A carat (abbreviated as “ct”) is a measure of a gemstone’s weight. It’s equal to 1/5th of a gram or 200 milligrams. You could also phrase that as five carats in a gram. A kilogram is 1,000 grams, or 5,000 carats.

(My apologies to those of you on the metric system. To Americans, this sometimes needs to be explained).

Gem weights are occasionally expressed in common fractions like ½ or ¼ carats but are more commonly expressed as decimal fractions. …

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