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.
Unique Facts about Africa: Origin of the Name 'Africa' Origin of the Name 'Africa' The name Africa came into Western use through the Romans, who used the name Africa terra â land of the Afri (plural, or Afer singular) â for the northern part of the continent, as the province of Africa with its capital Carthage, corresponding to modern-day Tunisia.