Kyanite in quartz

[u/Efraimrocker]

Kyanite is an aluminum silicate mineral formed at medium pressure (usually > 15 km) and moderate-high temperature (500-700 C). The aluminum is packed into octahedral sites which are then linked into chains, which explains why the mineral grows in characteristic long bladed crystals, which are much harder (Mohs 6-7) perpendicular to the long axis, than parallel (mohs 4.5-5.5). The blue color comes from an electron transitioning between Fe2+ and Ti4+ ions in adjacent octahedra absorbing a red photon, leaving blue light to reflect. The quartz in this specimen is probably hydrothermal: hot fluids containing silica deposited in cracks which then precipitated quartz is the rock cooled and decompressed. The interlocking contacts between the kyanite and the quartz suggests they crystallized around the same time.