Ahhh… gemstones each unique and beautiful on their own. I myself am fond of tourmalines, and diamonds (especially rough diamonds!) for their colors and unique textures. But it can be tricking buying a new stone if you are unfamiliar with what it is suppose to look like. Fortunately there is a common way to figure out the quality of stones. Let me be clear that diamonds are usually the easiest to compare when using this method as they are easier to distinguish in quality. The four C’s are…
Clarity refers to the transparency of gems. For example a diamond maybe of a lower clarity and be perceived as impure, that is why it is easier to distinguish. However other stones like emeralds almost always have an inclusion also known as a blemish. Like I said it is difficult to use this method because not all stones have such a distinguishing features like the diamond. The picture below shows the possible outcomes for a diamond.
How you shape the gem is also important. Each stone is usually cut so that it has the most optimal shape and reduces waste. So how can you distinguish the quality of a cut? The stone should almost look like it's dancing and all of its cuts are vivid. There should be no dark (extinction) or bright (window) spots.
Here is where it is very easy to tell a diamond apart. Color can come in a wide range among stones, even in the same kind. It is easy to see that a diamond of subtle yellow coloring will not be as valuable as a clear diamond. For colored stones it is important to look at hue, tone, and saturation. How deep is the color, does it have other colors, and if it is darker or brighter than the industry standard. These are all example you need to look for when picking colored stones
Carat refers to the weight of a stone and not the dimensions. It is possible to have two identical stones in shape but with different weights. In general prices for carat are set by the clarity, cut and color of a stone. And usually the larger a stone gets the more it tends to weigh and cost.
These are not the only quality determinants in stone, but they are the main and most likely used when it comes to pricing a gem.