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 initial Africans first set foot in the continent of America during or round about the age of the Egyptian Dynasties (btw 3100-2100 BC). According to recent study, it was d â¦ educed that they embarked on commerce voyages to and fro the continent supplying the channels with salt and precious metals.