Kyanit

Kyanite is a metamorphic mineral that is an aluminum silicate with the chemical formula Al2SiO5. It is a relatively common constituent of many metamorphic rocks, especially those formed under high pressure, such as schists and gneisses. Kyanite is also found in some sedimentary rocks.

The mineral is named from the Greek word "kyanos," meaning blue, referring to its typical color. While blue is the most common hue, kyanite can also be colorless, white, gray, green, or black. Its color is often unevenly distributed, with darker blue streaks or patches. Kyanite exhibits strong pleochroism, meaning it appears to be different colors when viewed from different directions.

Kyanite has a unique characteristic of being harder on its cleavage surfaces than on its crystal faces. This property is unusual for minerals. Its hardness on the Mohs scale varies depending on the direction of measurement, typically ranging from 4.5 to 7. Kyanite has a characteristic bladed or prismatic crystal habit.

Due to its hardness and heat-resistant properties, kyanite is used in the manufacture of refractories, such as furnace linings and kiln furniture. It is also utilized in the production of ceramics and glass. In its gemstone form, kyanite is appreciated for its attractive blue color and is often faceted for use in jewelry, though its relative softness and tendency to cleave require careful setting and wear. Gem-quality kyanite is typically found in pegmatites and metamorphic schists.