Hard as Flint

A feather blew across the ground to him. It was not a crowโ€™s. Too long, too hard, too tapering. The quill that had rooted it to the dragonโ€™s flesh was black, and hard as flint. In all his life, heโ€™d neither heard nor dreamed of dragon feathers.

No Such Thing as Dragons
Philip Reeve

Reeve, Philip - No Such Thing as Dragons