Kyanite is typically a blue aluminosilicate mineral -rich metamorphic pegmatites. Kyanite in metamorphic rocks generally indicates pressures higher than four kilobars. It is commonly found in quartz. Although potentially stable at lower pressure and low temperature, the activity of water is usually high enough under such conditions that it is replaced by hydrous aluminosilicates such as muscovite , or kaolinite. Kyanite is also known as disthene, rhaeticite and cyanite.
Kyanite is a member of the aluminosilicate series, which also includes the polymorph andalusite. Kyanite is strongly anisotropic , in that its hardness varies depending on its crystallographic direction. In kyanite, this anisotropism can be considered an identifying characteristic.
At temperatures above 1100 °C kyanite decomposes into mullite via the following reaction: 3(Al2O3·SiO2) → 3Al2O3·2SiO2 + SiO2. This transformation results in an expansion.
Its name comes from the same origin as that of the color cyan , being derived from the Ancient Greek word κύανος. This is generally rendered into English as kyanos or kuanos and means "dark blue".