Natural diamonds take a long time to form and can be dangerous to harvest. The diamond on any given wedding ring is at least a million years old, and possibly more than a billion years old. The ones we can mine with current technology were formed deep in the Earth's mantle and spit up by ancient volcanic lava flows.

A synthetic diamond or engineered diamonds (also known as an artificial diamond, cultured diamond, or cultivated diamond) is diamond produced in an artificial process, as opposed to natural diamonds, which are created by geological processes. Synthetic diamond is also widely known as HPHT diamond or CVD diamond after the two common production methods (referring to the high-pressure high-temperature and chemical vapor deposition crystal formation methods, respectively). Lab created diamonds or engineered diamonds or synthetic can be grown under laboratory condition. Lab created diamods available in different colours. Lab created dimanids are less costly than the original diamonds. They are poduced in lab at  high heat and pressure. Small traces of elements are also added during the intial phase of diamond preparation. 

Source: seeker.com