The "starry" stones

There are " starry " stones. This reputation derives from asterism , an optical phenomenon that mainly affects sapphires and rubies . But garnets and quartz can also be affected by this peculiarity.

They are rutile inclusions which, due to the interaction with light, form a sort of star visible on the surface of the gem .

While ruby ​​and sapphire always show this effect with a crossing of three lines, garnet and quartz do it with two lines. The so-called "Black star" (Diopside) a black stone forms the same two-axis star.