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.
On average, African Americans are of 78 percent West African, 19 percent European and 3 percent Native American heritage, with very large variation between individuals.frican-American history starts in the 16th century, with Africans forcibly taken as slaves to Spanish America, and in the 17th century with African slaves taken to English colonies in North America.