Gemstones are generally evaluated based on what are called “the three Cs”.
Cut
Although there’s technically a distinction between the cut of a gemstone — the way it’s faceted — and the shape it ends up as, the word “cut” is typically used to describe the shape of a gemstone.
Below, you’ll see images of the most common shapes in which gemstones are cut. When it comes to diamonds, the round cut is one of the most common you’ll see because it is especially effective at showing off the stone’s sparkle. When it comes to emeralds, what’s called the “emerald” cut is probably the most commonly seen.
Color
The second “c” stands for color, which jewelers to characterize the purity and luster of a stone. In a diamond, colorless white stones are the most prized. These days, the majority of synthetic or created diamonds are still white, but they, and other diamond-stand-ins like moissanite, can be created in a wide variety of beautiful colors.
Though sapphires are often thought of as blue, this is just a name for the mineral corundum, and “fancy” natural sapphires can also be found in colors like yellow, purple, orange, green and teal. Interestingly, red varieties of corundum have their own designation: rubies. Meanwhile, a pink-colored corundum stone could either be called a sapphire or a ruby.
Clarity
The term clarity, the third “c” is fairly self-explanatory — it means how free of impurities the stone is. Impurities in the crystal formation can affect how sparkly a gemstone is. Lab-created stones, whether they’re diamonds, moissanite or cubic zirconia, are typically free of impurities.