Some Kyanite display a 4 rayed Star and are considered rare. Kyanite comes mostly in light to dark blue and also in green, brown or colorless. The striking feature is that hardness varies with direction.
Kyanite is a mineral infrequently cut as a gemstone. It occurs in light to dark blue, green, colorless and brown colors in a transparent form with the blue color being most used in gemstones. Kyanite is of interest because of the extreme variablity in hardness with direction. In one direction, the hardness is 4.5 and in the other it is 7. Very easy cleavage is encountered in one direction with a less perfect cleavage occurring at 74 degrees to the first. The finest gem quality Kyanite may be confused in appearance with spinel or blue sapphires from Burma. 
