Clarity

The clearer and cleaner the stone, the more dazzling and rarer it will be. Because diamonds are formed deep in the earth, they can have natural "birthmarks"–minute traces of minerals and other elements known in the trade as inclusions which make each stone unique. Clarity refers to the number, color, size, and position of these inclusions, which are measured on a GIA scale from completely flawless (FL) to visibly imperfect (I3).