From the Latin sapphiru (meaning “blue”), September’s birthstone is universally in demand. While ruby is the term for the red variety of the mineral corundum, sapphire represents corundum in every other color. In consumer studies, blue sapphires are consistently ranked as the most popular; but among connoisseurs, purple, pink, and pinkish-orange sapphires are more sought-after. Sapphires have long been linked to royal jewelry; it is believed the stone symbolized trust and loyalty. No wonder Prince William presented his mother Diana’s sapphire ring to his now-wife, Kate Middleton.