Hello everyone, this is my first time posting here. I found this strange rock(?) on the shore of Lake Michigan while vacationing in Manistee last weekend. It's chalky white in color and sparkles in the sunlight. It's slightly shorter than a AA battery and can be chipped away by my fingernail at the rough end. I've never seen something like it and thought I'd try to find someone who knows what it is. Is it just a lump of hardened sand? I have zero experience identifying rocks, so I apologize if this is a dumb question. Thank y'all in advance.