Star Rubies are cut in a smooth domed cabochon cut, which displays a 3-ray, six point star. The star is visible when illuminated with a single light source, and it moves across the stone as the light moves. This effect is called asterisms, caused by light reflecting off minuscule rutile needles, called "silk," that are slanted among the crystal faces. A star ruby or a star sapphire's value is based on two things, the first being the beauty and intensity of the color, and the second being the sharpness, and strength of the star. The star ruby is 9 on the Mohs hardness scale.