Kyanite

Mineral Name: Kyanite

Chemical Composition: Al2SiO5

Color: Most commonly, kyanite is blue but can also be white, gray, green, colorless, yellow or orange.

Streak: The streak of Kyanite is white or colorless.

Hardness: Kyanite’s hardness can range from 4-7 on the Moh’s hardness scale.

Cleavage/Fracture: The cleavage of Kyanite is perfect in 2 directions, though it is sometimes hard to see both due to the splintery nature of kyanite.

Crystal Form: Kyanite’s crystal form is most often found as thin, long bladed crystals, but can be found in a “V” shape, where two wedge-shaped crystal sheets converge to form the “V” shape or what is otherwise known as a butterfly twin (3).

Luster: The luster of Kyanite is vitreous to pearly.

Special Features: Kyanite has a very special feature of having 2 separate hardnesses; the hardness along the vertical axis will range from 4.5-5.5 in hardness (3). The hardness along the horizontal axis is a hardness of 6-7 (3)

Varieties: There are actually no other types quite like kyanite but there are polymorphs. A polymorph is a organism, inorganic object or material that can take on multiple forms. It is a copycat of sort.

Mineral Group: Kyanite is in the silicate group because it is composed of the elements silicon and oxygen in a tetrahedral form. This group is composed of minerals that contain various amounts of silicon on oxygen. It is also a nesosilicate. Nesosilicates are silicates where silica tetrahedra are isolated units unlike other groups that show paired silica tetrahedra (3).

Environment: Kyanite is formed by metamorphism; this is when there are changes to a rock caused by heat, pressure, or heated fluids. Kyanite is heavily associated with Barrovian metamorphism. Barrovian metamorphism begins with a clay-rich parent rocks, such as shale, and uses index minerals (like kyanite) and metamorphic zones to measure the intensity of metamorphism (1). Index minerals can form at a certain pressure and temperature and appear in this certain order from low temperature to high temperature: Chlorite, biotite, garnet, staurolite, kyanite, and sillimanite. This intense pressure that forms kyanite is associated with heavy tectonic conditions, like the formation of volcanic arcs and mountain building events (1).

Associated Rock types: Kyanite can be found sometimes in granitic pegmatites; although, kyanite is almost always found in metamorphic rocks such as schists, eclogite, gneiss and granulite.

Occurrence in North America: There are kyanite mines in Virginia, North Carolina, and Georgia.

Economic Uses: Kyanite is used mostly for jewelry. To make jewelry, the mineral sample must first be cut, though it has two hardnesses which makes it a more difficult mineral to cut (5). The hardness will dictates the cut, and only skilled gemstone cutters are recommended for the job. The mineral is cut in “en cabochon” or faceted gemstones, and most commonly in the shape of an oval, but can be cut in different shapes (5).

Industrial Uses: Kyanite is used in a wide variety of industrial goods. For example, because kyanite can stand such high temperatures, it is used in the production of molds for moldings of high temperature metals (2). In addition, kyanite is used in the production of brake shoes, clutch facings, cutting wheels, spark plugs, and also porcelain fixtures (2).

First Notable Identification: The name kyanite came from Abraham Gottlieb in 1789 (4). It roots from the Greek word “Kyanos”, which means blue. Kyanite also had a different spelling name of “Cyanite” given by the French, much used by mineralogists in the 19th-20th centuries.

How We Identified It: When we first laid our eyes on kyanite we found that it was a deep ocean color. Also, we found that kyanite had a splintery-look compared to the other minerals; kyanite looked like it was stuck together with glue.