Diamonds are made of carbon. All carbon containing minerals do not turn into diamond. Diamonds were formed in the earth thousands of years ago under extreme heat and pressure. This extreme heat and pressure in the earth transformed the carbon into crystals and turned it colorless. Although diamonds formed deep in the earth, volcanic activity is what brought them to the surface.
Most diamonds discovered on the surface in mining operations are at least one billion years old. When minerals mix with diamond in nature, it gives the diamond color. The raw diamond goes through a process of exploration, discovery and then cutting and polishing to appear in the shining state as seen in jewellery.