side track story:
one time driving in a little car on an interstate, a rather big stone...like large gravel size...fell off a truck in front of me and bounced up. I saw it since before the bounce and saw it coming. it was clearly coming for my head.... looked like a boulder...so much so that I reflex ducked down behind the wheel and dash. Sounded like someone hit the windshield hard with a baseball bat.
Not a crack...the only mark was a little chip in the glass surface about the size of a grain of sand. I drove that car a long time and it never cracked from that chip. It was a different hit, in a completely different area taht broke the windshield enough to force replacement
Another time, with the new windshield I think, or maybe it was even before the boulder strike (memory is fuzzy)...Anyway, I heard a little tink sound, like you would behind a truck with sand blowing off it. Just barely a sound at all, like one large grain of sand...or like a bug hitting the windshield... and I never saw a thing so it was small.... And I noticed a small crack a couple inches long up near the mirror. As my trip continued over the next couple hours, in the sun, the crack was just a bit longer every time I'd look at it. In a few hours time it ran nearly to the bottom of the glass.