Propadope61 wrote:What you have there is Basalt. It is about 3 1/2 billion years old. The circular indentation is formed when this volcanic rock was cooling a gas bubble escaped and left the divit.
I have a few or these that I have found, and use them as cigar snuffers or holders
Now you know the rest of the story
Prop
thanks for the info. Mine is pretty big, I'd say the dimension of the indent is approximately half a baseball.
BTW, since you seem like a rock collector. I have collected thousands (literally) of geodes around here. I have buckets of golf ball sized and dozens of softball sized. Mostly calcite and quartz. I even have a few that are bigger than footballs.