Cut
When it comes to diamonds, you want yours to light up the room. That's why it's best to choose a diamond that's well cut. Of the 4Cs, a diamond's cut has the greatest influence on its fire, sparkle and brilliance. Cut not only refers to shape of a diamond, but more importantly to its proportions (how the diamond's angles and facets relate to one another), symmetry (the precision of its cut) and polish (the condition of your diamond's surface).

All diamonds have five basic parts. The table is the uppermost facet, or the flat surface on the top of the diamond. The crown is the section of facets between the table and the midsection of the diamond. The girdle is the horizontal midsection and widest part of the diamond. The pavilion is the section of facets between the girdle and the bottom tip of the diamond. The culet is the bottom tip of the stone. A traditional round brilliant diamond consists of 58 facets, 33 in the crown and 25 in the pavilion.

In a well-proportioned and symmetrical diamond, light will enter and exit through the crown to the eye. A poorly cut diamond, however, allows too much light to escape through the sides and bottom. As a result, a diamond with a poor cut will appear dull, even if it has good color and clarity.

Most diamonds are available in three basic styles:
Brilliant-cut diamonds include round, oval, pear, heart, and marquise-cut diamonds.
Step-cut diamonds feature rows of facets positioned in a step-like fashion. Most step-cut
diamonds have four sides and a rectangular shape, such as emerald-cut and baguette.
Mixed-cut diamonds combine the qualities of the brilliant and step-cuts. The most popular
example is the princess-cut (or radiant-cut)
 
The shape you choose is really a matter of personal preference, and each has its individual advantages.
 
Round Brilliant-cut diamonds are by far the most popular choice. Its design has been developed over
the last hundred years. The round brilliant-cut best features a diamond's fire, sparkle and brilliance.
Princess-cut diamonds are gaining in popularity and offer a more contemporary look.
Marquise diamonds are especially flattering for women with slender fingers.
Heart-shaped diamonds are a truly romantic and unique choice.
Emerald-cut diamonds are excellent for women whose taste runs more to the classic.
Pear-shaped cut (or teardrop) offers a unique way to express yourself.
Oval-shaped diamonds have an original beauty and are preferred for women who want to break with tradition.