If there is one kind of mineral that Africa is best known for it is rare gem minerals. There are numerous locations throughout the continent that produce unique gem species found nowhere else or few other places worldwide. The bulk of Africa’s unique gemstones, particularly tanzanite, tsavorite, and spessartine come from Eastern Africa, particularly from Tanzania and Kenya. These minerals are all related to metamorphic activity that has chemically altered silica and trace element rich limestones and shales into gem bearing rocks. Many of these gemstones, particulalrly tanzanite are enhanced via heat treating and other methods considering the value of material showing the best blue color. When tanzanite is mined, it can be purple, green, brownish, or blue but is typically heat treated to a royal purple-blue color. This heat treatment is considered acceptable in faceted gemstones but reduces value of specimen material.
A new find of large spessartine garnets at Nani Hill, Loliondo, Tanzania has been very significant because it has been the first large discovery of this material in high enough quality for the gem and jewelry trade. The spessartines are of mandarin color and can reach around 5cm in diameter, though are often much smaller. It’s said that digging has only sorted through weathered material and no exploration of the remaining garnet bearing vein has been done.
Madagascar is an African nation coming into the mineral scene very strongly in recent years. The island nation, which lies off the southeastern coast of Africa is richly endowed with complex pegmatites, amethyst veins, rubies, sapphires, gorgeous agates, and more. Madagascar’s unusual pegmatite minerals are what have driven the popularity behind the nation’s minerals over the past decade and a half or so. Perhaps the most unique gem mineral from Madagascar is pezzotaite- a cesium containing mineral that is very closely related to beryl. It is found in fluorescent pink colored hexagonal crystals. While these crystals are very small and rare, they are extremely valuable. Madagascan tourmaline is also unique and gorgeous. Some of the more famous examples are deep cranberry to near scarlet colored. Many larger tourmaline crystals from Madagascar have black , opaque exteriors and must be carefully sliced to expose the gemmy interior. Often large crystals are prepared into many thin, coaster-like slices that expose gorgeous zoning patterns inside of the crystals.
Many other exotic kinds of material have been coming from Africa in recent years. Some nations in Africa have started to produce specimens for the first time and they are quite different than what many are used to seeing from the continent.
For example, Malawi has produced many interesting minerals that are a result of volcanism associated with Africa’s Great Rift Valley. Unusual silica undersaturated magma has risen here to an altitude where volatiles in it form bubbles which form into pockets. These are often lined with unusual minerals such as smoky quartz, arfvedsonite, aegirine, zircon, microcline, and others. Specimens of this kind from Malawi are becoming quite popular.
Zambia also has been producing interesting minerals recently, though it has been long known for fine copper minerals and an unusual occurrence of zinc minerals at the Broken Hill Mine in Kabwe. Zambia’s Kagem Mine, which is an extremely large open pit emerald mine is known to produce fine euhedral gemmy emeralds embedded in quartz matrix. New localities in Zambia have also yielded amazing cirtrines, rutile, ilmenite, davidite, and aquamarine. It’s definitely a country which I expect to produce many more minerals in the future.