Rare Forms From Ballast Point Tampa Florida Miocene Corals And Associated Reef Life Bulletin 56

This is a lemon sized Montastrea whose exterior features are eroded.  It felt so light I thought for sure it was a thin-walled, even eggshell thin crystalline geode, instead was this, another intriguing and more rare circumstance.  This is what all the coral did after the reef became silted over, it eroded from the inside out, leaving holes, casts, in the surrounding clay/limestone.  Fluctuating water levels and associated flooding and drying of layers over the eons is credited with inundating the coral layer with silica suspended in water, creating geodes from the coral shaped voids in the clay/rock.  This head did not fossilize as most did on The Gadsen Peninsula, but the interior exhibits graphically what the geode forming voids looked like during formation of most Tampa material near Ballast Point.

 

If you right click a picture, then choose "Open In Another Tab", then left click on that, you will see biggest version.

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This is a type I am still working on, it is slightly odd, I can't fit it into anything I have seen about Ballast Point.