Green Rock ID

[SAShew]

Found this green rock in a field in Southeast Illinois. Anyone know what it is? It has not been polished, just rinsed off the dirt.

 

[Broken knee]

Crack a piece off and see what it looks like inside could be quarts or serpentine?

 

[ToddsPoint]

I think that is a type of porphyry. Maybe diabase porphyry? The white crystals are called phenocrysts. Lots of different flavors of porphyry. Here's one from the net. I live in Cent. IL and this stuff is common in the glacial till. Gary