re: home insurance on granite countertops

HO Comprehensive policy covers any sudden and accidental damage unless it's excluded in the policy.

Named Peril policy covers only damage caused by the listed perils in the policy. Like Fire, Wind, Lightning, Hail, ect.

No idea what policy the OP bought. Named Peril is usually on low value or rental dwellings, unless you shopped the policy as give me the cheapest insurance that will satisfy the Lien Holder.

Edit to add
An exclusion that could apply to your loss would be faulty material or workmanship. Read you policy.