noun. I think it's connected to the trenchant bone and the laconic bone.
Real citation: "3. 'My novel is x thousand words but it reads longer'. If you don't know why this is funny, need to sharpen your Sardonica bone."
(April 27, 2007, Miss Snark, the literary agent, http://misssnark.blogspot.com/2007/04/slow-night-at-toaster.html)
Made-up citation: "There's no treatment in the world that will repair a damaged sardonica bone, local doctors deadpanned."