The potash deposits in the Republic of the Congo are the largest in Africa. The other large reserve is in Ethiopia.
Madagascar has the world’s largest known accumulation of flake graphite deposits. Continuations of these high-quality deposits in Mozambique and southeastern Kenya contain further reserves of graphite.
While deposits of low-grade sand suitable for construction and engineering work are widely distributed, reserves of sands with a sufficiently high silica content for glass manufacture are more localized. There are deposits in western Africa (Côte d’Ivoire, Liberia, Nigeria, and Ghana), East Africa (Uganda and Tanzania), and South Africa. Glass sands are also found in Egypt.
Kyanite (cyanite), a mineral aluminum silicate used as a refractory, occurs most typically in Southern Africa. Apart from South African reserves, there are deposits in Kenya, Malawi, Ghana, Cameroon, and Liberia.
Of the abrasive substances, industrial diamonds are most closely associated with Africa. The continent contains some 40 percent of the total world reserves. The stones are found in a number of major belts south of the Sahara. The principal known reserves of diamonds in their primary form are in the South African Vaal belt. Elsewhere in Africa, primary deposits are found in Tanzania, Botswana, and Lesotho.
Another major belt of diamondiferous rocks encircles the Congo River basin and includes the world’s largest deposit, located in the Democratic Republic of the Congo, which contains the majority of Africa’s reserves of industrial diamonds. The same belt has secondary deposits that occur elsewhere in that country as well as in the Central African Republic and Angola. In western Africa known reserves are located primarily in alluvial gravel fields. They are found in Sierra Leone, Guinea, Côte d’Ivoire, Liberia, and Ghana.
A considerable proportion of the world reserves of corundum (a common mineral, aluminum oxide, notable for its hardness) is located in Southern Africa. The principal deposits are in Zimbabwe, South Africa, Mozambique, Madagascar, and Malawi.
Pumice is found in areas of volcanic activity such as the Atlantic islands, the coastal Atlas Mountains of northeastern Morocco, and the East African Rift System, notably in Kenya, Tanzania, and Malawi. Joint reserves, however, constitute only a small percentage of the world total.
Reserves of building materials are characterized by their wide distribution, to such an extent that the commercial status of such deposits depends more on their location relative to areas of development than on their extent and quality. While almost all African countries have reserves of building materials, knowledge of such reserves is strictly related to the country’s level of development, and no meaningful estimate of the size of reserves can be made.
Granite is located in Morocco and Nigeria, and there are vast reserves in Burkina Faso. Quartzite (a granular rock, consisting essentially of quartz) is important as a building stone in Uganda and the Democratic Republic of the Congo. Dolerite (a coarse-grained basalt) is produced in South Africa and basalt, which is crushed for use in road construction, in Senegal. Marble is found in Mali, Togo, Nigeria, and South Africa.
Limestone is important because of its use in the cement industry, and deposits are fairly widespread. North Africa is a particularly important source. In western Africa a belt of limestone runs from the Central African Republic to the Atlantic coasts, with major outcrops in northern Nigeria, Niger, Burkina Faso, and Mali. Elsewhere there are deposits in Nigeria, Benin, Togo, and Ghana. East African deposits include those in Kenya, Tanzania, Uganda, and Zambia; there are also deposits in South Africa.
North Africa has major reserves of gypsum on the Mediterranean coast, as well as in outcrops along the Gulf of Suez and the Red Sea. Somalia has one of the largest known deposits. Eastern Africa and Madagascar have further reserves, and in western and Southern Africa superficial deposits are particularly important—for instance, north of Nouakchott, Mauritania.
Many of the major deposits of the most important commercial gem mineral, the diamond, have already been described above in the discussion of industrial diamonds. One major deposit, however—that of Namibia—consists almost entirely of gem diamonds.
There is no other gem mineral in Africa of comparable importance to these diamond reserves. Deposits of a number of such stones are found, however, especially in Southern and eastern Africa, where diamond fields contain beryl, garnets, amethyst, rose quartz, topaz, opal, jasper, emeralds, and other stones. Madagascar contains a large deposit of garnet. Tourmaline is found in Madagascar and Namibia. Agate is particularly associated with the volcanic areas of eastern and Southern Africa and malachites with the Katanga Copperbelt, while sapphires are found with diamonds in Ghana.
Africa contains no major world deposits of talc, but the mineral is found in Morocco, Nigeria, Sudan, Zimbabwe, and South Africa. Reserves of asbestos are much more important, and Southern Africa has a number of deposits of world significance.
Major deposits of fluorite, or fluorspar (a common mineral, calcium fluoride, used as a flux in metallurgy), are particularly associated with deposits of lead and zinc. In South Africa the chief deposit is in the northeastern part of the country. North African reserves lie primarily in Tunisia and Morocco.
Africa produces a very small share of the world supply of diatomite (a fine siliceous earth, used as an abrasive). The most important deposit is in Kenya. Water resources
In general, the seasonal distribution of river flow in Africa reflects the seasonal rainfall pattern; the amount of groundwater entering the river channels during the dry season is comparatively small. Important modifications in the flow of some rivers are caused by the presence of large lakes and swamps, which act as natural storage reservoirs, by the construction of dams on their courses, and by the incidence and severity of drought. Surface water
Although the surface area of Africa is about one-fifth of Earth’s land surface, the combined annual flow of African rivers is only about 7 percent of the world’s river flow reaching the oceans.
North Africa’s few perennial rivers originate in the mountains of the Maghrib, and their water is used extensively for irrigation. The large number of wadis, or ephemeral watercourses, to be found throughout the Sahara and the eastern Mediterranean coastal lands become filled with water as a result of the rare and erratic storms that occur over mountainous areas; otherwise they remain dry.
From the relatively well-watered areas of western and equatorial Africa, the Sénégal, the Niger, the Logone–Chari, and the Nile rivers flow through the drier inland zones. Of these, the Niger River, originating in the Fouta Djallon region of Guinea, is retarded in the lake and swamp area south of Timbuktu in Mali, and the Logone–Chari feeds Lake Chad.
The Nile, the world’s longest river, receives more than 60 percent of its water from the Ethiopian Plateau, although its source is much farther south in the mountains of Burundi. Since the completion of the Aswan High Dam, only a small proportion of the river’s total flow reaching Egypt enters the Mediterranean Sea.
A number of rivers flowing in a more or less southerly direction into the Atlantic Ocean drain the southern part of western Africa. Many flow rapidly over bedrock before entering the coastal plains, draining into the system of lagoons and creeks along the coast. During the dry season the upper reaches of these rivers are without water, but in Guinea, Sierra Leone, and Liberia, where the dry season is fairly short, the rivers flow throughout the year.