A diamond's size is described in millimeters (mm). These measurements are roughly comparable to carats. A 1-carat round diamond is typically 6.5 mm, while a 1.25-carat round diamond is 6.8 mm. For square-cut diamonds like princess, cushion, and asscher, 1-carat is typically 5.5 mm and a 1.25 carat is 6 mm.
Diamond color is all about what you can’t see. Diamonds are valued by how closely they approach colorlessness – the less color, the higher their value. (The exception to this is fancy color diamonds, such as pinks and blues, which lie outside this color range.) Most diamonds found in jewelry stores run from colorless to near-colorless, with slight hints of yellow or brown.
The GIA Clarity Scale contains 11 grades, with most diamonds falling into the VS (very slightly included) or SI (slightly included) categories. In determining a clarity grade, the GIA system considers the size, nature, position, color or relief, and quantity of clarity characteristics visible under 10× magnification.
The GIA Cut Grading System applies to the most popular cutting style – the standard round brilliant – and all clarities across the D-to-Z color range. There are five cut grades: Excellent (EX), Very Good (VG), Good (G), Fair (F) and Poor (P). A diamond with an Excellent cut grade is very bright.14-Jan-2016