A rare piece of volcanic history. These pieces were in the ocean for millions of years and when volcanic action happened the cells died and was replaced by whatever material was near by. Many have a glass like surface.
I am tumbling these Tampa Bay coral pieces for over a month. Before starting the rock is gray, craggy and rough for the most part. Never know how it will come out and there is a lot of waste. Not the same as tumbling a smooth rock to begin with.
And there is a lot of variety. Always fun to open the tumbler. Good for unusual designs or as a specimen collectible