If the grain is vertical, you are going to have a harder time. This also applies to breaking wooden baseball bats. Increase the thickness and decrease the length for a greater challenge. I find the knifehand best suited to this technique. After getting comfortable with wood breaking, this is a good introduction to brick breaking.
Patio blocks are common in brickyards, garden stores, and big chain hardware stores.
Home Depot has them almost all the time. 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.