what shape is a brick.
Any shape the mold-maker wants it to be.
http://www.mathsisfun.com/definitions/rectangular-prism.html
A brick is a rectangular prism shape. It has six faces, including a front face, a back face, a top face, a bottom face, and two side faces. The front and back faces are usually larger than the side faces, giving the brick its recognizable shape. To confirm the shape of a brick, you can also visualize or recall the common shape of bricks that you have seen or touched.
If you have access to a brick or a picture of a brick, you can easily determine its shape visually. Look for a rectangular object with distinct front and back faces, as well as smaller side faces.