Blue kyanite (disthene) on a pedestal (1-6 kg) from Araçuai, Brazil.

The mineral kyanite, or disthene, is an aluminium silicate with the chemical formula Al₂SiO₅.. It belongs to the group of nesosilicates. The blue, grey, white, green, or black mineral has perfect cleavage along the crystal plane [100], a white streak colour, and a vitreous to pearly lustre. The crystal system is triclinic, the average density is 3.61, and the hardness is 4 to 7. Kyanite is neither magnetic nor radioactive. The name of the mineral kyanite is derived from the Greek word kyanos, meaning "blue". Kyanite is a very common mineral as a component of many rocks. It occurs, among other things, in metamorphosed sedimentary rocks. It is also, together with the other aluminium silicates sillimanite and andalusite, an indicative mineral for the depth and temperature at which a rock has undergone metamorphism. Kyanite is usually stable at temperatures below 650 °C and at pressures above 0.3 GPa (gigaPascal). The pressure and temperature are related, so that at high pressure (0.6 GPa), a higher temperature (600 °C) is needed to form sillimanite from kyanite. At pressures below 0.3 GPa, andalusite is the stable aluminium silicate. Gemstone-quality kyanites occur in India, in the gemstone deposits in Myanmar and Korea. In the United States, kyanites are mined in California, Tennessee, Georgia, New Hampshire and North Carolina. In Africa, kyanite occurs in Kenya and Tanzania; in Europe in Russia, Switzerland, Austria and France. Kyanite occurs in the sand fraction of Dutch Quaternary river sediments. In the heavy mineral analysis that took place in the Netherlands at the National Geological Service during the second half of the twentieth century, the mineral is classified in the so-called stable group. In this research, only the name disthene is used.