Rock chips from "Bi Valves?" I wouldn't expect calcium carbonate or magnesium carbonate could have enough specific gravity or density to crack a windshield?. Gotta be some chunky crustaceans! {ha ha, sorry micro paleo talk... just can't help myself}
Funny you should mention Florida though. Last trip home from work down the Alaska highway, 3 weeks ago, I had a Floridian, massive, motor home dropping tools out of a carrier on the back rack that just trashed my windscreen. I think it was a Craftsman 3/8s' drive that came screaming at me. I managed to get the "nomads" pulled over near Pink Mountain and told him... Nice guy, felt terrible and offered to pay. As we go thru 2-4 windscreens a year up here and mine was already heading home to be replaced I thanked him but declined. Kinda funny really, 3 months ago I was watching North American Bald Eagles heading south and now all I see are North American motor homes heading north... and I mean a LOT of motor homes Lol.
Another post here suggested a "hardex" coating to help...... well as Mohs' hardness scale tell you, fused quartz has a hardness of 6-7, {out of 10} and our sharply angular, "gravel", comprised of chert arenites to pre-cambrian granite have a hardness of some where in the boron nitride feldspathic quartz ranges 6-8+, combined with terminal velocity of said rock, {I'm sure some bright young engineer could x,y / xx,y calculate impact numbers}... well the result of a painted coating as well as the surface hardness of the glass would logically make this idea somewhat of a "snake oil solution". {I did try it on a previous vehicle, {Hummer H3 SUT} that had a catchers mitt for a windshield}, and the results were what I expected. It was good for repelling rain though..
My 2 bits and sorry for being so verbose and long winded.... just couldn't resist. Lol