Gut-sick again this morning, so this will probably be my only post for today.
I think Joe Dirt and Bologna321 are on the right track. I notice one side of the object has what looks to me like "semi-conchoidal fracture" breakage. The opposite side shows the "dried-mud lakebed" cracking pattern mentioned by Bologna321. So, to my eye, it looks like a mineral or substance that possesses conchoidal or semi-conchoidal fracture (such as Asphalt, glass, Obsidian, etc) which was previously molten and while molten fell onto a dried-mud lakebed, creating an impression of the lakebed's cracked surface on its underside.
As to the identity of the mineral or substance... to my eye, it looks like Asphalt (a mineral whose natural color varies from shades of dark-brown to black).