Marialite

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Marialite
Marialite-169082.jpg
Marialite
General
Category Tectosilicate
Formula
(repeating unit)
Na4Al3Si9O24Cl
Strunz classification 09.FB.15
Crystal symmetry Tetragonal 4/m
Unit cell a = 12.06Å, c = 7.572(3) Å; Z = 2
Identification
Color Colorless, white, grey; pink, violet, blue, yellow, brown, orange-brown, pale green or reddish
Crystal habit Typically flat, pyramidal striated crystals; massive, granular
Crystal system Tetragonal; crystals are usually prismatic
Cleavage Distinct on {100} and {110}
Fracture Uneven to conchoidal
Tenacity Brittle
Mohs scale hardness 5½–6
Luster Vitreous, pearly, resinous
Streak White
Diaphaneity Transparent to opaque
Specific gravity 2.55–2.74
Density 2.5–2.62 g/cm3
Optical properties Uniaxial (-)
Refractive index nω = 1.539–1.550 nε = 1.532–1.541
Birefringence δ = 0.007 - 0.009
References [1][2][3][4]

Marialite is a silicate mineral with a chemical composition of Na4Al3Si9O24Cl[3][4] if a pure endmember or Na4(AlSi3O8)3(Cl2,CO3,SO4) with increasing meionite content.[1] Marialite is a member of the scapolite group and a solid solution exists between marialite and meionite, the calcium endmember.[1] It is a rare mineral usually used as a collector's stone. It has a very rare but attractive gemstones and cat's eye.[5]

Crystallography[edit]

Marialite has tetragonal crystallography and a 4/m crystal class. It has a 4 fold rotation with 90° mirror planes. Crystals are usually prismatic with prominent forms of prisms and dipyramids.[6]

Marialite belongs to an uniaxial negative optical class which means it has one circular section and a principal section shaped like an oblate sphenoid.

Discovery and occurrence[edit]

Marialite was first described in 1866 for an occurrence in the Phlegrean Volcanic complex, Campania, Italy. It was named by German mineralogist Gerhard vom Rath for his wife, Maria Rosa vom Rath.[2][3]

Marialite occurs in regional and contact metamorphism: marble, calcareous gneiss, granulite and greenschist. It also occurs in skarn, pegmatite and hydrothermally altered volcanic rocks.[2][3] This means that Marialite is formed in high pressure and/or high temperature environments.

References[edit]

  1. ^ a b c Klein, C., and Dutrow, B. (2007) The 23rd Edition of the Manual of Mineral Science, 675 p. John Wiley and Sons, Inc. Hoboken, New Jersey, U.S.A.
  2. ^ a b c Handbook of Mineralogy
  3. ^ a b c d Mindat.org
  4. ^ a b Webmineral data
  5. ^ http://www.galleries.com/minerals/silicate/scapolit/scapolit.htm
  6. ^ Johnsen, O. (2000) Photographic Guide to Minerals of the World. 439 p. Oxford University Press, Great Clarendon Street, Oxford