Kyanite is a mineral with a hardness of 5 out of 10 on the Mohs scale of mineral hardness [?]. These Triclinicly structured gems are made of aluminum silicate, their full chemical compound being Al2SiO5.
Kyanite is an aluminum silicate that occurs as elongated and tabular in groups of light-blue crystals darker toward the center, or flat, bladed crystals in schists and gneisses, or as radiating rosettes in quartz. It is trimorphous with sillimanite and andalusite.
Kyanite is also known as disthene, meaning, "double strength." This refers to the fact that the hardness along the length of kyanite crystals is less than the hardness across them. has three different hardnesses in three different crystallographic directions. This is the mineral's most characteristic feature.
It appears with a blue color, sometimes white or colorless at margins. It is transparent to translucent, with a vitreous luster, pearly on cleavage surfaces. It is infusible, and insoluble in acids.
The most valued colors are deep cornflower blue, pale azure blue, and bluish-green. The color is often in irregular streaks.
Like the other aluminum silicate polymorphs, kyanite is an indicator of metamorphic conditions.
It is found almost exclusively in pelitic rocks rich in aluminum, and metamorphosed under high pressure (mica schists, gneisses, eclogites, and amphibolites), associated with garnet, staurolite, and corundum. It is occasionally found in pegmatitic veins running through these rocks, and common in emery deposits and concentrated in sands produced by the breakup of crystalline schists.
Splendid blue crystals with staurolite and paragonite are from Pizzo Forno (Switzerland); Gray crystals with radiating structure from Val di Vizze and Val Passiria (Bolzano, Italy), the Tyrol (Austria), Morbihan (France) and more rarely in rocks round Musso (Como, Italy); enormous opaque blue crystals from Minas Gerais (Brazil); green crystals up to 30 cm long from Machakos (Kenya); large deposits in the USA, also India, and Australia.
Cat's-eye kyanite is a dark blue to pale blue variety of kyanite that exhibits chatoyancy, when cut en cabochon.
Chrome kyanite is a green, chromium-rich variety of kyanite found in Sakha, the Russian Federation.
Other names for kyanite include cyanite, beril azul, and sappare.
It is sometimes confused with aquamarine and sapphire.
Kyanite derives its name from the Greek "kyanos" meaning "a dark blue substance."
Kyanite is mined in several parts of the world for use as refractory material. Transparent crystals are occasionally used in jewellery. The crystals are difficult to cut because of their variable hardness and cleavage.
It is also a raw material for the manufacture of high-temperature porcelain products, perfect electrical insulators and acid-resistant products, including hydrofluoric acid.
It is very important as a means of identifying grade and type of metamorphism in the host rock.