Purchase sandstone from a quarry or stone material supplier, about 128 cubic inches per brick.
Use a sledgehammer to break up any large chunks of sandstone. Pulverize about one-third of the sandstone. The remaining sandstone can be coarsely ground, provided no pieces are larger than 1/2-inch in diameter.
Build a brick mold by making a rectangular frame from two pieces of 3-by-8-by-1-inch wood and two pieces of 3-by-4-by-1-inch wood. Connect the pieces using two nails or screws in each corner.
Mix the pulverized sandstone with water in a 5-gallon bucket to create a cement-like bonding paste for holding the bricks together.
Mix in coarsely ground sandstone until the mixture is sufficient to fill the mold. The mixture should pour from the paint bucket when shaken but should not drain out on its own. It should resemble the consistency of thick brownie mix.
Pour the mixture of sandstone and paste into the mold, shaking it several times to prevent air bubbles that weaken the brick structure. Allow the brick to set in the sun until dry. The amount of time depends on the time of year and the exposure to sunlight.
Remove the brick from its mold and present your brick with accompanying papers or visual aids to your teacher.