Whoops - I needed to pan down - that's a beautiful coral with quite unusual preservation!
It looks like its been partly replaced by silica which is tough and chemically resistant - the normal calcite preservation (like in the other pebble) wouldnt survive on a beach and would look bruised.
Thank you again.
It looks like Mulder or Scully would have had more than a passing interest in it!
It looks very organic and fresh.
How old would such a thing be and, further, I'd it unusual to keep such a vivid colour?
It's likely to be from the Carboniferous - what your looking at are the walls of the coral which have been replaced by silica - the colour is most likely caused by Iron Oxides.
The likely scenario for this fossil is that the original calcite coral skeleton was buried and the surrounding material was compressed and formed rock. For normal fossils this would be the end of the story.
In your case at some point in the last few hundred million years the calcite skeleton was dissolved by acid leaving a coral skeleton shaped hole which was later filled by a silica rich solution.
Its very pretty and the silica has preserved a lot of detail - nice find!