Marialite

Marialite is a silicate mineral with a chemical composition of Na4Al3Si9O24Cl[4][5] if a pure endmember or Na4(AlSi3O8)3(Cl2,CO3,SO4) with increasing meionite content.[2] Marialite is a member of the scapolite group and a solid solution exists between marialite and meionite, the calcium endmember.[2] It is a rare mineral usually used as a collector's stone. It has a very rare but attractive gemstones and cat's eye.[6]

Marialite
General
CategoryTectosilicate
Formula
(repeating unit)		Na4Al3Si9O24Cl
Strunz classification9.FB.15
Crystal systemTetragonal
Crystal classDipyramidal (4/m)
(same H-M symbol)
Space groupI4/m
Unit cella = 12.06 Å, c = 7.572(3) Å; Z = 2
Identification
ColorColorless, white, grey; pink, violet, blue, yellow, brown, orange-brown, pale green or reddish
Crystal habitTypically flat, pyramidal striated crystals; massive, granular
CleavageDistinct on {100} and {110}
FractureUneven to conchoidal
TenacityBrittle
Mohs scale hardness​5 1⁄2–6
LusterVitreous, pearly, resinous
StreakWhite
DiaphaneityTransparent to opaque
Specific gravity2.55–2.74
Density2.5–2.62 g/cm3
Optical propertiesUniaxial (-)
Refractive indexnω = 1.539–1.550 nε = 1.532–1.541
Birefringenceδ = 0.007 - 0.009
References[1][2][3][4][5]

Crystallography

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.[7]

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

Discovery and occurrence

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.[3][4]

Marialite occurs in regional and contact metamorphism: marble, calcareous gneiss, granulite and greenschist. It also occurs in skarn, pegmatite and hydrothermally altered volcanic rocks.[3][4] This means that Marialite is formed in high pressure and/or high temperature environments.

References
  1. Mineralienatlas
  2. 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.
  3. Handbook of Mineralogy
  4. Mindat.org
  5. Webmineral data
  6. http://www.galleries.com/minerals/silicate/scapolit/scapolit.htm
  7. Johnsen, O. (2000) Photographic Guide to Minerals of the World. 439 p. Oxford University Press, Great Clarendon Street, Oxford
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