Rock/Fossil ID ?

[willace walliam]

Found this yesterday... Looks like it could be fossilized coral or sponge on one side. It has a lot of quartz on the other side.... or its just a rock... I have no idea. Anyone have any ideas?

[DrJill]

Interesting looking rock but ...

Fossils are only found in sedimentary rocks and that doesn't appear to be one.

The dark material looks to be volcanic in origin. Appears to be fine grained, which indicates it cooled rapidly, probably on the surface. As it cooled, it cracked.

Likely it was subsequently buried by additional eruptions.

Later, the white material bubbled up and filled all the cracks.

BTW ... you can find fossil corals and sponges along the banks of the river in the Twin Cities

[willace walliam]

thanks for the reply DrJill. I posted some picks on a fossil forum and they said it was just a rock also. oh well