Formation and Delivery to the Surface

As you learned in Diamond Essentials, diamonds owe their incredible durability and beauty to their formation process. Formation under just the right temperature and pressure conditions results in the crystal structure that causes diamond’s supreme hardness and desirable optical properties. If there’s a slight variation in temperature or pressure, or if the diamonds take too long to reach the surface, the result is graphite, not diamond.

Once gem-quality diamond crystals are delivered to the surface, they often survive millions of years of battering in rivers, streams, and ocean tides. Many are even incorporated into new sedimentary rocks, re-released into the environment by weathering, and transported many hundreds or thousands of miles without significant damage.

That’s the case with the diamonds of Namibia, on the western coast of Africa. The diamonds arrived at the earth’s surface millions of years ago in the African interior. Then the forces of erosion released the diamond crystals from the rocks around them and the gems were gradually washed westward in the Orange River to the Atlantic Ocean, creating what might be the world’s largest deposit of gem-quality diamonds.

Estimates of the number of diamonds on and near the coastline run as high as 1.5 billion carats. Experts also think that between 90 and 95 percent of them are gem quality. The percentage is high because crystals with large fractures and other structural defects don’t survive the journey between the continental interior and the ocean. Only the strongest gems make it.

Offshore diamond resources are some of modern diamond mining’s newest frontiers. You’ll learn about the technology that makes undersea diamond mining possible in Assignment 6.