Replacing a dilapidated fence, moving the dirt around, instead of the usual rocks and pieces of concrete, etc. my hoe came up with what appears to be an unusual brick. The cross section is virtually identical to a current 2x4, it's a lot longer than the usual brick, it's 11 3/8" long. It's heavy! 4 lb. 12 oz. It's so dense at first I wondered if it was steel, partly because the geometry is so perfect. The sides are slick, the corners very square. I suppose it's not as dense as steel, but it seems very heavy. The color is reddish, there is a lot of black on it, as from a shiny black paint. Is this some kind of archeological artifact, a brick from 80 years ago or something? My house was built in 1910. I've been living here for decades, dug in the soil a lot (I garden), never seen anything like it.