Sapphire is crystallized Aluminium Oxide. It will show up perfectly clearly in X-ray; it just won't show in a metal detector.

Although very hard, sapphire is not tough, and cleaves very easily along certain crystal planes. Various sorts of tools, like kitchen knives and scissors are available made out of fine grained engineering ceramics; these can be as tough as steel and much harder. The phrase to look for is "Transformation toughened zirconia".