Andalusite is an

aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

nesosilicate Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, the crystalline forms of silica (silicon dio ...

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...

with the chemical formula Al₂SiO₅. This mineral was called andalousite by Delamétherie, who thought it came from

Andalusia Andalusia ( , ; , ) is the southernmost autonomous communities of Spain, autonomous community in Peninsular Spain, located in the south of the Iberian Peninsula, in southwestern Europe. It is the most populous and the second-largest autonomou ...

, Spain. It soon became clear that it was a locality error, and that the specimens studied were actually from El Cardoso de la Sierra, in the Spanish province of

Guadalajara Guadalajara ( ; ) is the capital and the most populous city in the western Mexican List of states of Mexico, state of Jalisco, as well as the most densely populated municipality in Jalisco. According to the 2020 census, the city has a population ...

, not Andalusia. Andalusite is trimorphic with

kyanite Kyanite is a typically blue aluminosilicate mineral, found in aluminium-rich metamorphic pegmatites and sedimentary rock. It is the high pressure Polymorphism (materials science), polymorph of andalusite and sillimanite, and the presence of kyani ...

and

sillimanite Sillimanite or fibrolite is an aluminosilicate mineral with the chemical formula Al2SiO5. Sillimanite is named after the American chemist Benjamin Silliman (1779–1864). It was first described in 1824 for an occurrence in Chester, Connecticut ...

, being the lower pressure mid temperature polymorph. At higher temperatures and pressures, andalusite may convert to sillimanite. Thus, as with its other polymorphs, andalusite is an

aluminosilicate Aluminosilicate refers to materials containing anionic Si-O-Al linkages. Commonly, the associate cations are sodium (Na+), potassium (K+) and protons (H+). Such materials occur as minerals, coal combustion products and as synthetic materials, of ...

index mineral, providing clues to depth and pressures involved in producing the host rock. Round faceted andalusite 1

Varieties

The variety

chiastolite Chiastolite ( ) is a variety of the mineral andalusite with the chemical composition Al2SiO5. It is noted for its distinctive cross-shaped black inclusions of graphite. The presence of these crosses caused the mineral to be used as a gem. Chias ...

commonly contains dark inclusions of carbon or clay which form a

cruciform A cruciform is a physical manifestation resembling a common cross or Christian cross. These include architectural shapes, biology, art, and design. Cruciform architectural plan Christian churches are commonly described as having a cruciform ...

pattern when shown in cross-section. This stone was known at least from the sixteenth century, being taken to many European countries, as a souvenir, by pilgrims returning from Santiago de Compostela. Viridine is a

green Green is the color between cyan and yellow on the visible spectrum. It is evoked by light which has a dominant wavelength of roughly 495570 nm. In subtractive color systems, used in painting and color printing, it is created by a com ...

variety of andalusite in which

manganese Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...

3+ substitutes for aluminium, the same change is also responsible for the colour. Kanonaite is a greenish-black mineral related to andalusite and having the approximate composition . A clear variety found in Brazil and Sri-Lanka can be cut into a gemstone. Faceted andalusite stones give a play of red, green, and yellow colors that resembles a muted form of

iridescence Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear gradually to change colour as the angle of view or the angle of illumination changes. Iridescence is caused by wave interference of light in microstru ...

, although the colors are actually the result of unusually strong

pleochroism Pleochroism is an optical phenomenon in which a substance has different colors when observed at different angles, especially with Polarization (waves), polarized light. Etymology The roots of the word are from Greek (). It was first made compou ...

Occurrence

Andalusite is a common

metamorphic Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...

mineral which forms under low pressure and low to high temperatures. The minerals

and

are polymorphs of andalusite, each occurring under different temperature-pressure regimes and are therefore rarely found together in the same rock. Because of this the three minerals are a useful tool to help identify the pressure-temperature paths of the host rock in which they are found. It is particularly associated with

pelitic A pelite () or metapelite is a metamorphosed fine-grained sedimentary rock, i.e. mudstone or siltstone. The term was earlier used by geologists to describe a clay-rich, fine-grained clastic sediment or sedimentary rock, i.e. mud or a mudstone, t ...

metamorphic rocks such as

mica schist Schist ( ) is a medium-grained metamorphic rock generally derived from fine-grained sedimentary rock, like shale. It shows pronounced ''schistosity'' (named for the rock). This means that the rock is composed of mineral grains easily seen with a l ...

. The world's highest concentration of andalusite is found in the Glomel mine in

Côtes-d'Armor The Côtes-d'Armor ( , ; ; , ), formerly known as Côtes-du-Nord until 1990 (, ), is a department in the north of Brittany, in northwestern France. In 2019, it had a population of 600,582.France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...

) which accounts for 25% of the global production of this mineral.

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

possesses the largest portion of the world's known andalusite deposits.

Uses

Andalusite is used as a

refractory In materials science, a refractory (or refractory material) is a material that is resistant to decomposition by heat or chemical attack and that retains its strength and rigidity at high temperatures. They are inorganic, non-metallic compound ...

in furnaces, kilns and other industrial processes.

References

{{Authority control Aluminium minerals Nesosilicates Orthorhombic minerals Minerals in space group 58 Industrial minerals Gemstones

Varieties

Occurrence

Uses

See also

References