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.
The term Afro-Latin American refers specifically to people of African ancestry and not to European ancestry, such as Sub-Alpine European white. The term is not widely used in Latin America outside academic circles. Normally Afro-Latin Americans are called black (Spanish: negro; Portuguese: negro or preto; French: nÃ¨gre or noir).