Paragonite

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Paragonite
ParagoniteWithGarnet 3392.jpg
Paragonite with Garnet
General
Category Phyllosilicates
Micas
Formula
(repeating unit)
NaAl2[(OH)2|AlSi3O10]
Strunz classification 09.EC.15
Identification
Color Colorless, pale yellow, grayish, grayish white, greenish, light apple-green
Crystal habit massive, fibrous or scaly
Crystal system Monoclinic (2/m) Space Group: C 2/m
Twinning common on the [310] less common on the {001}
Cleavage Perfect on the {001}
Fracture Micaeous
Tenacity Elastic
Mohs scale hardness 2.5 - 3
Luster Pearly
Streak White
Diaphaneity transparent to translucent
Specific gravity 2.78
Optical properties Biaxial (-)
Refractive index nα = 1.564 - 1.580 nβ = 1.594 - 1.609 nγ = 1.600 - 1.609
Birefringence δ = 0.036
Dispersion r < v strong
Ultraviolet fluorescence None
References [1][2][3]

Paragonite, also known as Natron-Glimmer, is a mineral, related to muscovite. Its empirical formula is NaAl2[(OH)2|AlSi3O10]. A wide solvus separates muscovite from paragonite, such that there is little solid solution along the vector Na+K+ and apparent micas of intermediate composition is most commonly a microscopic (or even sub-microscopic) intergrowth of two distinct micas, one rich in K, and the other in Na. Paragonite is a common mineral in rocks metamorphosed under blueschist facies conditions along with other sodic minerals such as albite, jadeite and glaucophane. During the transition from blueschist to greenschist facies, paragonite and glaucophane are transformed into chlorite and albite.[4]

It was first described in 1843 for an occurrence at Mt. Campione, Tessin, Switzerland.[2] The name derives from the Greek, paragon, for misleading, due to its similar appearance to talc.[3]

References[edit]

  1. ^ Mindat
  2. ^ a b Webmineral
  3. ^ a b Handbook of Mineralogy
  4. ^ Deer, W. A., et al. (2006). Rock-forming minerals, Volume 3A Micas (2 ed.). Geological Society of London. p. 302. ISBN 978-1-86239-142-0.