Rear view miror cracked

[Chris Lovell]

When I unearthed the '88 Cab from winter storage, the rear view mirror has a new vertical crack near the center of the mirror. This is the damndest thing as I know the mirror was untouched during storage. Can anyone think of a reason the mirror would just crack in a straight line? The stored car was certainly subject to deep cold but there was no radical fast temperature changes over the winter. The only other thought was the car was stored in a storage bag with desiccant (moisture remover). I can't imagine that would have any effect. Anyway, I guess I'm seeking a new mirror unless someone tells me I can change the glass or some other fix.
Thanks,
CL