The star sapphire and star ruby are the rarest and most valuable of their kind. The patterns of moving stars that shine within them have an otherworldly quality—perfectly symmetrical and moving in light. There is no doubt that they are the most expensive and set in the best jewelry, but what makes the stone in it a “star”?
Star stones form impressive patterns due to a phenomenon called starlight, which comes from the ancient Greek word for star. During the formation of the stone, it included a homogeneous admixture of titanium dioxide contained in the mineral rutile. These fine threads, commonly known as “silk”, run throughout the stone, giving the starstone its creamy, translucent color.
When light hits a star stone, the stone’s base material and rutile impurities refract light with different refractive indices. It is this dichotomy that causes the light to form into thin, needle-like dots that coalesce at the core of the stone.
Star power is not set in stone. It is formed by the movement of light, which changes when the stone is viewed from different angles. Opal exhibits a similar phenomenon called opalescence, in which silica bands within the stone reflect light at different wavelengths, causing the inner color to shift between extremes.
Star patterns form most easily in corundum, the mineral from which sapphires and rubies are formed. Although all rubies are red, their color ranges from dark red blood red to an almost neon hot pink. Sapphire can be more varied. The most recognizable is dark blue, but there are also yellow, green and pink sapphires.
Star patterns can form on all colors of corundum, as well as other gemstones. These formations are rare, but stellate impurities are noted in garnet, diopside, and spinel.
While rutile inclusions are the most easily identifiable cause of the bright white star pattern, the stone can also contain hematite impurities resulting in a darker star pattern. The stone can even contain both rutile and hematite and have two stars at the same time, forming a 12-pointed star instead of the standard six-pointed star.
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Post time: Sep-05-2022