Guess what I was doing today?

Decided to start laying the flooring. Heavy work moving things about.
I moved with the times and started off using a handsaw, then became more adventurous- used an electric saw. I like to live dangerously. I'm hopeless at DIY, but enjoy trying.I thought I'd move on to a loc style laminate, to save the mess of glue getting everywhere. I've only managed to do 1/2 the kitchen so far. All was going well until I moved the washing machine. I found this bit of ?stone/cement. I think from the WM. Can anybody help? Is it safe to use. I switched the empty machine on for a short cycle. It sounds ok, and seems to spin and drain etc.

I've not even gone over the doorstep today- what a waste.

I'm going back to B&Q tomorrow for covers for the base legs of the drawer units, for a wee change.and I'm not going to any more floorstuff for a couple of days to give my back a rest.