The main character is a young girl, moody, sent to live with a family member (possibly aunt and cousin). She’s a bit of a troublemaker and/or lies a lot. – She sits on a fence outside and sees an old lame mare in the field. A man (named Joe, says “Aye” a lot) who owns the horse chats to the girl and gets a pebble out of the horse’s hoof to stop her lameness. – The girl likes this unusual pebble and keeps it on the windowsill in her room because the light hits it nicely. – The pebble grows and eventually falls off the windowsill. – It gets so big she and the other girl (her cousin?) have to lump it into a wheelbarrow and get it away from the house, where it tips the barrow and eventually explodes into many pebbles. Read between 1990 – 2005 in the UK.