There are some minerals which are extremely similar to one another and this rock is a good example.

This agate-like material has the skin of chert/flint on the outer edge. Beneath the flint is a semi opaque material with the same conchoidal fracturing as chalcedony and some quartz. It has bubbles of other unknown material in it and hints at banding around a window.

It could just be brownish chalcedony.

This could be cut, polished, or used to make knapped arrowheads. Either way you will be left with something pretty.