Carat
Some people believe that carat refers to the size of a diamond while in actuality; carat is the term used to measure a diamond's weight. A carat is equal to 200 milligrams, and there are 142 carats to an ounce. One carat is made up of one hundred points. The larger the diamond, the greater its rarity. Because larger diamonds are more rare, they generally have a greater value per carat.
Clarity
Internal imperfections and external irregularities affect the clarity of the diamond by interfering with the passage of light throughout the stone. Imperfections such as spots, lines, or bubbles are known as inclusions. The diamond is more valuable when it has fewer inclusions. According to the GIA's quality analysis system, clarity is graded on a scale ranging from flawless (FL or IF) to imperfect (I). The system is based on the visibility of inclusions at a magnification of 10x.
Confidence
While these are the 4 most recognized C's, a fifth and less recognized, yet equally important C does exist. That is Confidence. Confidence in your jeweler is extremely important when buying this piece of jewelry that will last forever, and be passed down among generations. It is important to shop at a professional jeweler, one that is a member of a professional trade association such as Jewelers of America (JA). JA requires high ethical standards of its members and provides them with ongoing education.