what is this round black rock contained in sandstone

2018-08-14 16:04:02

Wondering what this rock is, found in the spring mountains near las vegas nevada. It is a hard smooth feeling black rock which appears to be surrounded with sandstone, the black rock goes all the way through the sandstone. Also found a similar round black rock contained in a harder stone at the same location, this one has an angular rough surface and does not go all the way through the surrounding rock. Thanks!!