Natural vs. Synthetic: Natural Sapphires that are pink, purple or blue can at times be diamagnetic. Therefore gems of these colors cannot reliably be distinguished by magnetic response from synthetic Sapphires. However, natural blue Sapphires most often do show a weak to moderate magnetic response due to iron, and such responses definitively separate them from synthetic blue Sapphires, which are always inert (diamagnetic). We can say that any magnetic attraction rules out synthetic origin for blue Sapphire, but a diamagnetic response does not rule out natural origin.