I'm not sure what it is, the size, color and shape is different than most old bricks I'm familiar with. I think it may be a chunk of sand stone, possibly burned. Hand made bricks have been around for centuries. In the pioneer days they were fired in brick "clamps", where the bricks were part of the clamp, or kiln. The inner bricks were hardened and the outer bricks remained softer, but all brick were red. If the inner bricks were exposed directly in the fire they could develop a black really hard glaze on that side. My farm included a brick clamp from the 1850's that made most of the bricks for the buildings in the township. It's interesting to see the variation in the bricks.