The differences in clay is most noticed by color from the iron oxides. Both types have it, but it is more obvious in states of the south. It may have to do with glaciers that overran the northern states like Indiana thousands of years ago.
The brick on top is Pigeon Forge, Tennessee red clay. The other three are Flora, Indiana brown clay. Fired in the same kiln for 9 hrs to 1875deg F. Notice the difference in shrinkage.
Heres the address if you are interested in why some clays are so much more red than brown, yellow, or grey.