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Four aspects of gemstone grading determine the per-carat value of a ruby, including color, clarity, cut and carat. Quality of a top-grade ruby means it has rare features, rather than being labelled as better than another... More »

Tips for estimating ruby prices per carrot include measuring gemstone size, inspecting for visible defects and assessing the color of the stone. Color is the most important factor for estimating value. Stones that are pu... More »

Tanzanite costs between $50 and $650 per carat as of 2015. Factors determining the cost include the quality of the stone and its relative size. The quality of the final cut also affects its value. More »

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Naturally black diamonds are extremely rare and can have a very high value, depending on the cut, color, clarity and carat size of the diamond. The most accurate way to learn the value of a black diamond is to have it ap... More »

To determine the value of a diamond, note its color, clarity, cut and carat. Diamonds are more valuable when they have less color, lack spots and imperfections, have higher cut grades and weigh more. Compare each of thes... More »

As with other gems, the value per carat of tanzanite is influenced by color, cut and clarity. Other factors jewelers use to grade tanzanite include shape and polish. More »

Determining the quality of a diamond involves the consideration of its cut, clarity, color, carat size and certification. Certification through an accredited organization, such as the American Gem Society or the Gemologi... More »