A common mistake is confusing Cut with Shape. Every Diamond Shape has its Ideal Cut. The percentages of table and depth along with other measurements can be calibrated so that you can see how brilliant each diamond will be.
Years ago diamonds fell into only 3 categories...A, B, & C. Today we are privileged with the ability to classify diamond color on a more advanced spectrum of absence of color.
All Diamonds, aside from Flawless and Internally Flawless, have birthmarks (inclusions) which they are born with. Based on the type, size, amount, and placement of the inclusions each diamond is given its clarity grade.
Carat is the unit of measurement used to describe the diamond weight and size. Its a unit of weight for diamonds and precious stones, equal to 200 milligrams
Diamonds come in a variety of shapes ranging from the classic Round Brilliant all the way to the Sleek Asscher cut with Emerald, Princess, Cushion, Pear, Marquise, Radiant, Oval, and even the Heart shaped within the spectrum.
A Laboratory Certificate is important when buying a diamond. It should be provided by highly regarded third part laboratory. Some examples are GIA, EGL, and AGS.