shell less partially formed egg, help

So far only my Black Star is laying regularly.  The Bluebelle and the Amber Lee have each laid just one egg each and that was a couple of days ago for both of them.  Today I found what looked like lightly poached egg white on the ground, it was a sort of loose sausage shape and had a very small unformed egg shaped centre that was also soft (tiny yolk that never got to be full sized, or another egg?).  I don't know who laid it.  They're all eating well and lively and they have plenty of grit which I put in a pot but mix with their layers mash and corn so I know they're getting it.  Is this young birds just getting acclimatised to laying or should I worry?

Thanks Scabs, Sookie hen kept pecking at it too, so I moved it!