Andalusite is an aluminiumnesosilicatemineral with the chemical formula Al2SiO5. This mineral was called andalousite by Delamétherie,[3] who thought it came from Andalusia, 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, not Andalusia.[4]
Andalusite is trimorphic with kyanite and sillimanite, 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 index mineral, providing clues to depth and pressures involved in producing the host rock.[5]
The variety chiastolite commonly contains dark inclusions of carbon or clay which form 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.[7]
Viridine is a green variety of andalusite in which manganese 3+ substitutes for aluminium, the same change is also responsible for the colour.[8][9]Kanonaite is a greenish-black mineral related to andalusite and having the approximate composition (Mn0.76Al0.23Fe0.02)AlSiO5.[10]
A clear variety found in Brazil and Sri-Lanka can be cut into a gemstone.[11] Faceted andalusite stones give a play of red, green, and yellow colors that resembles a muted form of iridescence, although the colors are actually the result of unusually strong pleochroism.[12]
Occurrence
Andalusite is a common metamorphic mineral which forms under low pressure and low to high temperatures. The minerals kyanite and sillimanite 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 metamorphic rocks such as mica schist.[13]
The world's highest concentration of andalusite is found in the Glomel mine in Côtes-d'Armor (France) which accounts for 25% of the global production of this mineral.[14]South Africa possesses the largest portion of the world's known andalusite deposits.[15]
Uses
Andalusite is used as a refractory in furnaces, kilns and other industrial processes.[16]
^Delamétherie, Jean Claude (1798). "Sur une pierre de l'Andalousie". Journal de Physique, de Chimie d'Histoire Naturelle et des Arts. 46: 386–387.
^Calvo, Miguel (2018). Minerales y Minas de España. Vol. IX. Silicatos. Madrid, Spain: Escuela Técnica Superior de Ingenieros de Minas de Madrid. Fundación Gómez Pardo. pp. 91–94. ISBN978-84-8321-883-9.
^Whitney, D.L. (2002). "Coexisting andalusite, kyanite, and sillimanite: Sequential formation of three Al2SiO5 polymorphs during progressive metamorphism near the triple point, Sivrihisar, Turkey". American Mineralogist. 87 (4): 405–416. Bibcode:2002AmMin..87..405W. doi:10.2138/am-2002-0404. S2CID131616262.
^Whitney, D.L. (2002). "Coexisting andalusite, kyanite, and sillimanite: Sequential formation of three Al2SiO5 polymorphs during progressive metamorphism near the triple point, Sivrihisar, Turkey". American Mineralogist. 87 (4): 405–416. doi:10.2138/am-2002-0404.
^Calvo, Miguel (2016). "El "lapis crucifer", "piedra de cruz de Compostela": un elemento importante de los patrimonios geológico y cultural del NW de España". De Re Metallica. 6: 67–79.
^Abs-Wurmbach, I.; Langer, K.; Seifert, F.; Tillmanns, Ε. (1 October 1981). "The crystal chemistry of (Mn 3+ , Fe 3+ )-substituted andalusites (viridines and kanonaite), (Al 1-x-y Mn x 3+ Fe 3+ y ) 2 (O|SiO 4 ): crystal structure refinements, Mössbauer, and polarized optical absorption spectra". Zeitschrift für Kristallographie - Crystalline Materials. 155 (1–4): 81–114. doi:10.1524/zkri.1981.155.14.81. S2CID201671728.
^Vrána, S.; Rieder, M.; Podlaha, J. (1978). "Kanonaite, (Mn 0.76 3+ Al0.23Fe 0.02 3+ )[6]Al[5][O|SiO4], a new mineral isotypic with andalusite". Contributions to Mineralogy and Petrology. 66 (3): 325–332. doi:10.1007/BF00373417. S2CID95925117.