Kyanite (dysthene)

Kyanite (or disthene) is a mineral composed of aluminum silicate (Al₂SiO₅), recognizable by its elongated crystals with magnificent deep blue hues, but can also be white, green, gray, or black. It forms in metamorphic rocks subjected to high pressures and has a rare peculiarity: its hardness varies depending on the crystal direction.

The most beautiful specimens come notably from Brazil, Nepal, Switzerland, and the United States, where they are prized for their elegant crystals and intense color.