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.
For African and African descended people of Hispanic/Latino heritage living in, or native to, the United States, see Black Hispanic and Latino Americans. Afro-Latin Americans or Black Latin Americans refers to Latin American people of significant African ancestry. The term may also refer to historical or cultural elements in Latin America thought to have emanated from this community.