Calcite?

This lump of chalk, with what I think are layers of calcite, was picked up from the woodland floor at the nature reserve. It was very near an old overgrown chalk pit that used to supply a lime kiln nearby. I'm used to finding fossilised sponges and sea urchins (echinoids) - often in the spoil heaps outside badger setts - but I haven't found anything quite like this before.