Any and all Gems are almost always cut, to enhance their beauty and display their color.
The Brilliant is a cut made especially for the Diamond, designed so that light enteri… wait, you can go read that part on my post on the Diamond; “Everyone’s best friend!” Lapidaries are people who cut Gems, but people find it hard to cut Diamonds, being the hardest stone (on the Mohs scale, 10) that they specialize only on Diamonds; so they call themselves “Diamond cutters” (not a very long or “fanciful” word, is it?)
The Rose cut is designed to show the color of the stone and make the facets (cuts) look beautiful, like a Rose, and is usually used on a Sapphire.
The Step cut, also known as the Emerald cut, is made mainly to show the Color of the stone, which is ideal to use on Amethysts (as in the photo) as well as the usual Emerald (as the name proves).
The Cabochon is a dome, Star Sapphires must be cut as Cabochons to see the the star, and opaque stones, such as the Turquoise in the picture are almost always cut as Cabochons because for any of the other cuts, light must be able to travel through the stone to have any effect. I am in a club that grinds stones into Cabochons, and I have made a few already, but I will blog about that later.
These are the four main cuts, and the stones in your jewelry will be most likely be cut in one of these.