This rock would be called an Organic Sedimentary rock .
This rock is a sedimentary rock. When I received this rock many years ago it was said it came from a town called Coalinga, CA. It came from an open field. The town is situated about 100 miles east of the ocean. Upon further research the area of Coalinga use to be an ancient sea bed. So, the possibility it came from Coalinga, Ca, can be true.
The reason you can tell it's a sedimentary rock is by the texture of it. Mostly, all sedimentary rocks have layers or strata. Sedimentary rocks can sometimes collect various organisms bones or shells that undergo some recrystallization in ground water. This becomes a fossil.