2 Metaphors for brittle

A melancholy man would find here matter to work upon, to see heads as brittle as glasses, and often broken; men come hither to quarrel, and come hither to be made friends: and if Plutarch will lend me his simile, it is even Telephus's sword that makes wounds and cures them.

Is it to be endured, I say, that this rock should prove as brittle as sand, and that those who held this language should come down in a week after, and say, give us two millions and a half to subsidize Germany, and then we shall have a better army than we had with Russia?

2 Metaphors for  brittle