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 mostly African group is substantially African, as 70% of African Americans in this group have less than 15% European ancestry. The 20% of African Americans in the mostly mixed group (2.7% of US population) have between 25% and 50% European ancestry.he mostly African group is substantially African, as 70% of African Americans in this group have less than 15% European ancestry. The 20% of African Americans in the mostly mixed group (2.7% of US population) have between 25% and 50% European ancestry.