This is a little chunk of I think fossilised coral, or maybe just dead coral, picked up from a beach, probably highly illegally, in Barbados just over a year ago.
Tiny Tuesday theme is imprint or stamp and this has imprints of tiny creatures which lived long ago.
The structure is beautiful. I’ll blip it from farther away one day to give an idea of the pattern on it, each little round bit is only a couple of millimetres across.