Amicite

Amicite is a silicate mineral of the zeolite family. It has a general formula of K₂Na₂Al₄Si₄O₁₆·5(H₂O).^[4] Amicite was described in 1979 from specimens obtained at the Höwenegg quarry in Immendingen, Hegau, in the German state of Baden-Württemberg, which is consequently its type locality.^[5] The name is in honor of Giovanni Battista Amici (1786–1863) a botanist, physicist, optician, and inventor of microscope optical elements.

Amicite
General
Category	Zeolite
Formula (repeating unit)	K2Na2Al4Si4O16·5(H2O)
IMA symbol	Ami[1]
Strunz classification	9.GC.05
Crystal system	Monoclinic
Crystal class	Sphenoidal (2) (same H-M symbol)
Space group	I2
Unit cell	a = 10.26, b = 10.43 c = 9.90 [Å]; β = 88.32°; Z = 2
Identification
Formula mass	690.51 g/mol
Color	Colorless
Twinning	none
Cleavage	none
Fracture	Conchoidal
Luster	Vitreous
Streak	White
Diaphaneity	Transparent
Specific gravity	2.18
Optical properties	Biaxial
Refractive index	na = 1.485, nb = 1.490, nc = 1.495
Birefringence	0.01
References	[2][3]

Structure and optical properties

Amicite is monoclinic, so the crystallography has three axes of unequal length and the angles between two of the axes are 90 degrees and one is less than 90. Amicite is also pseudotetragonal with a = 10.23, b = 10.43, c = 9.88, and d = 89, and belongs to the space group I2.It appears as small colorless crystals, formed by the rhombic prisms {110} and {001}, combined in such a way that the crystal appears to be a dipyramid.^[6]

Amicite is classified as biaxial anisotropic so the velocity of light varies depending on direction through the mineral, as well as showing double refraction. The index of refraction is the geometric ratio of the angle of light entering the crystal (angle of incidence) over the angle the light is bent when it enters the crystal (angle of refraction). The index of refraction can be defined mathematically as n=velocity of light in a vacuum/velocity of light in the mineral. Amicite has three indices of refraction na = 1.485, nb = 1.490, nc = 1.494. A minerals birefringence is defined as the difference between the highest and lowest index of refraction, amicite's birefringence is 0.009.

Amicite is a zeolite mineral, the commercial uses of zeolites are a function its three distinct properties: absorption, ion exchange, and catalysis. Zeolites are also known for their ability to absorb and lose water without any effect on its crystal structure.

Occurrence

Amicite is a very rare mineral, known only in four locations in the world, the type locality, the Vostochnyi and Kirovskii mines in the Chibiny massif, Murmansk region (Russia), where the largest known crystals come from,^[7] and also the quarry from Las Urracas, on the El Arzollar volcano, Campo de Calatrava (Ciudad Real).^[8] In addition to being poorly distributed, it is very scarce in the four locations mentioned.

References

1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
2. Barthelmy, David (2 November 2010). "Amicite Mineral Data". Mineralogy Database. 1997–2010. Retrieved 5 November 2010.
3. Ralph, Jolyon; Ida Chau (5 November 2010). "Amicite". Mindat.org. 1993–2010. Retrieved 5 November 2010.
4. "Handbook of Mineralogy" (PDF). Mineralogical Society of America. 2004.
5. Alberti, A.; Hentschel, G.; Vezzalini, G. (1979). "Amicite, a new natural zeolite". Neues Jahrbuch für Mineralogie - Monatshefte: 481–488.
6. Tschernich, Rudy S. (2013). Zeolites of the World. Geoscience Press Inc. pp. 39–42. ISBN 978-0-945005-07-0.
7. "Kirovskii apatite mine. Mindat".
8. Viñals, J.; Calvo, M.; Sanz, A.; Martí, J. (2013). "Zeolites and associated minerals in the vacuoles of some of the Campo de Calatrava volcanoes – Ciudad Real, Spain". Mineral up. 3 (4): 54–69.

• Alberti, A.; Vezallini, G. (1979). "The Crystal Structure of Amicite, a Zeolite". Acta Crystallographica. B35 (12): 2866–2869. doi:10.1107/S0567740879010852.