This entry is a typical example of the influence of polymorphs on mineral properties. As a high-alumina silicate mineral, the kyanite group minerals have excellent fire resistance and calcination volume expansion properties, making them important in applications such as refractory materials. They also have significant significance in terms of their genetic mineralogy. Based on previous literature and the work of the author of this handbook, the crystal-chemical characteristics and basic properties of kyanite group minerals are introduced as follows.