Answer: kyanite

AnswerCrossword Clue
kyanitea mineral, also CYANITE
kyanitemineral, aluminum silicate, Al2SiO5, occurring in blue or greenish bladed triclinic crystals, used as a refractory
kyanitean aluminum silicate mineral Al2SiO5 that occurs usually in blue thin-bladed triclinic crystals and crystalline aggregates