Sapphire

A sapphire is the mineral corundum, the same as ruby, but colored blue by iron and titanium. Sapphires come in many colors, from yellow to pink, but blue is the best known. They are very hard, so they last a long time in rings.

Some sapphires show a star of six rays, because tiny needles of another mineral inside reflect the light. The star is called an asterism, and it moves as the stone or the light moves. Tap it to catch the star: its rays spread out from a bright center, it glides across the top, and the rays draw back in at the far side.