The six-rayed-star effect shimmers best over the surface of the stone when moved in daylight. Star ruby can often be distinguished by its pleochroism, which means that the color varies with the viewing angle. Black Star Diopside belongs to the magnesium based Diopside group of minerals that form in metamorphic and igneous rocks. The six-rayed-star effect appears most clearly under natural light. Star sapphire can be distinguished from other forms of sapphire by its unique asterism. So ideally, there should be enough rutile to create a distinct star whilst maintaining good color. Ideally the color should be equivalent to a non-star specimen of the gem, but the presence of rutile in the stone tends to weaken the color. But asterism may also be exhibited by a number of other gemstones, such as moonstone, quartz, spinel, citrine, diopside, emerald, garnet and chrysoberyl.Ĭolor is also very important in a star gemstone. The most famous examples are star sapphire and star ruby. Asterisms are found very rarely in a small number of gem types cut as cabochons. These are gems that exhibit special optical called an asterism or star effect. In the gemstone world there are a special group of gems known as phenomenal gemstones.

Black star of india gem