Criteria that determine the value and rarity of a gemstone are cut, carat, clarity, and color. Some stones are purely clear, colorless, but others have a slight tone of yellow, that can decrease their value. Black stones also known as carbonados are rarer than the regular clear ones. Their specificity is that they do not reflect light, but capture it. Therefore, when speaking of a black gemstone, we do not do it in terms of fire, scintillation, and brilliance. Their value is determined by using criteria like: size, clarity, purity, and intensity of color.
Black rocks are different from other rocks, not only due to their color, but also due to their chemical composition. A black diamond is made up from small carbon crystals. They have a polycrystal structure, meaning they are as harder as the clear ones, but more fragile. Some rocks are treated to become black, by using a process called irradiation. Specialists make it become dark green, so it can be easily seen if a gemstone is naturally or artificially black. Such type of dark green shade is never seen in a natural black gemstone.
Specialists will sometimes color a high quality diamond that has a dirty color into black to increase their value and be able to use them in jewelry. Because as mentioned before, diamonds with a dirty color are not so valuable and rare. In an artificially colored gemstone, the dark green shade can be seen when natural light reflects on it in a certain way. Artificially colored gems will never be pure black, a shade of dark green or even brown. Artificially colored gemstones like fancy green, yellow, and red contain a single crystal.
Black gemstones can be made up from one single crystal or from many crystals and then is called carbonados. When buying them, you should be careful to ask for an authenticity certificate, so you know if it is colored naturally or artificially, and to which processes it suffered.
Diamonds should be bought only if they have a Kimberley certificate and even a history to track down the jewel. If you choose to pay a huge sum of money on gemstones, because everyone knows they are very expensive, you have to make sure it’s authentic ad not a fake.
This is the reason why you should ask for an authenticity certificate, a history of the rock. You have to be aware that the diamond you intend to purchase is colored naturally or artificially. This is important because you have to know exactly its value. Moreover, you have to know its value so you can pay the correct price for it.