They're not stone, this has been posted in the wrong forum category. I'll move it over.
Chicken tiles were made by Johnsons Tiles in the, what, 80's?
And accidentally the pattern on the front if put the right way up would look like chickens. Although they weren't meant to be, and some fitted them in a random direction, customers did used to complain and assume they were all meant to go with the chicken standing the right way up.
I'll try to find you a picture.
Some horrible colours back then. Seen loads of tiles on top of tiles in kitchens, and when you pulled off the first layer, chicken tiles were under them. I bet that's happening less and less these days though. I've not seen it mentioned for a long long time lol so you might just be the last!!