Chemical weathering is the process by which rocks are broken down by chemical reactions. There are different types of chemical weathering. Hydrolysis is the chemical breakdown of a substance when combined with water. The most common example of hydrolysis is feldspar in granite rocks changing to clay.
Racially Africans originated in Africa, Europeans in Europe and so on. (before that the human species originated in Africa, but that's ancient history) African Americans are an ethnic group, or a subrace of the African race.
Most African Americans are of West and Central African descent and are descendants of enslaved blacks within the boundaries of the present United States. However, immigrants from African, Caribbean, Central American, and South American nations and their descendants may or may not also self-identify with the term.n average, African Americans are of 78 percent West African, 19 percent European and 3 percent Native American heritage, with very large variation between individuals.