Aggregate means when you break one open, it has rock particles in it to reinforce it. These blocks often come in gray, red, and sometimes green. They can be flat on both sides or the bottom can have ridges. The color and ridges make no difference. These blocks can easily support your weight plus a couple of your friends, so don't be disappointed if you find them difficult to break.
Patio blocks are good for their consistency in difficulty, although a wet block is harder to break.
They are usually left in the rain in brickyards so let them dry out a few days after you buy them. This applies for any sort of manufactured block or brick. Try any technique you wish but believe it or not, the iron palm works the best. Work up to two or three blocks without spacers. If you can break two or three, your hand is dangerous.