Kyanite belongs to the class of silicates. Derived from Aluminum silicate, Kyanite is polymorph with mineral andalusite & sillimanite i.e. they have similar chemistry but different crystal structure. Mineral kyanite has typical blue colour & wide variation in hardness, which can be called its unique characteristics. It's hardness may vary from 4-7.5 in the same specimen crystal. Usually, Kyanite found in rocks that are formed in high pressure conditions that is to say metamorphic rocks.
Although it has characteristic blue colour, Kyanite may be green, yellow, white.
 

There are three polymorphs of Al2SiO5: andalusite, kyanite and sillimanite. These three minerals form in aluminous metamorphic rocks. The temperature and pressure are what determines which of these polymorphs will crystallize. Kyanite is typically found in rocks that formed under conditions of high pressure regional metamorphism. Kyanite most often occurs in high pressure regionally metamorphosed aluminous rocks and in the quartz veins that cut through them, associated with quartz, muscovite, almandine garnet, biotite, staurolite and corundum. It also occurs in some kimberlite pipes and eclogites associated with pyrope garnet and omphacite. The blue color in metamorphic kyanite is due to trace amounts of Fe+2 and Ti+4 impurities substituting for aluminum. The light blue color of kyanites found in kimberlites is due to trace amounts of chromium.