Tanzania obtains much of its gem wealth from a geological feature known as the Mozambique Orogenic Belt, which contains one of the richest gem loads on earth. The Belt runs in a north-south direction through the eastern part of the country and it is up to 300 kilometers wide in places. The rocks in this mountain belt have undergone significant tectonism and metamorphism, which has created a multitude of gemstones, including sapphires.

The majority of the sapphires from Tanzania are found in three locales: the Umba River Valley in the north, and Tunduru and Songea in the south.

The gem gravel of the Umba River Valley has been a major source of fancy sapphires for at least half a century. The area yields sapphires in all colors of the rainbow, including highly valued padparadschas and rare color-change sapphires. The finds are usually facetable grade and some of the stones are sizeable. Sapphires from Umba may be distinguished by their boehmite needles, which are found along rhombohedral twining planes.

Fine sapphires have been produced at Tunduru since the mid 1990s. The gem gravel in this area yields a range of blue, pink, purple, and green sapphires.