Unlike stone’s shape, which is its outline visible from above, the cut refers to the relationship between the sizes of different parts of a stone, as well as to the position, shape, and proportions of its facets.
Important to distinguish between a stone’s cut and its cut “grade”
GIA which is the supreme authority on every aspect related to diamonds has an extensive material on the subject publicly available on their web site.
We are not going to reiterate the information, if you are are interested in learning the subject in-depth please visit their web site.
What we are interested here are the fine points that every consumer must know in order to choose the right diamond.
• Brilliant vs. step cuts - read more
When diamond facets are triangular, diamond-cut or kite-shaped the stone is said to have a brilliant cut.
Stones with brilliant cut are: round, oval, modern cushion, marquise, radiant, heart and pear shapes.
When facets are square or rectangular and run parallel to each other in “steps” the cut is referred to as a “step-cut”.
The only step cut stones are Emerald and Asscher cuts.
Stones used to “accessorize”- side stones for example, could be faceted as brilliants or step cuts. For example half moons, baguettes, trapezoids can be both, however baguettes are much more common as step cuts and majority of half moons have brilliant facets.