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.
Immigrants born in Africa constitute 1.6 percent of the black population. People of the African immigrant diaspora are the most educated population group in the United States â 50 percent have bachelor's or advanced degrees, compared to 23 percent of native-born Americans.