This block was on a pallet of what was called corkstone that i bought to use in a pond nearly 20 year's ago, I used the rest to border my koi pond but this one was too cool to pu into the water. i had it indoors for many year's but it got moved outdoors and developed a lot of moss, ,while it still looked cool i recently hit it with a pressure washer revealing more than had shown prior and since have become more curious about the center dis and cluster of spines. this morning I used a little sandblasting to erode the backside and this is what i have. I have no way to know were it came from,and suggestions? is it already too cool to mess with furthermore or do you think there's more to be seen?