Kyanite is an attractive mineral that has a near sapphire like blue color in some especially nice specimens. Kyanite has a unique characteristic in that it has a wide variation in hardness, in the same crystal . The hardness of kyanite is approximately 4.5 when scratched parallel to the long axis of the crystal and approximately 6.5 when scratched perpendicular to or across the long axis. Other minerals usually have variable hardness on different crystal faces due to a different concentration and oreintation of the atoms in the structure. Diamond is one such mineral, a fact gem cutters take advantage of often.
Color is blue usually but also can be white, gray or green.
Color is often not consistent throughout the crystal and can be blochy or in streaks. Luster is vitreous to almost pearly. Transparency crystals are transparent to translucent. Cleavage is good in one direction parallel to the flat pinacoid face. Fracture is splintery.