Apophyllite

Apophyllite
General
CategoryPhyllosilicate
Formula
(repeating unit)		(K,Na)Ca4Si8O20(F,OH)·8H2O
IMA symbolApo[1]
Crystal systemTetragonal
Space groupP4/mnc
Identification
ColorUsually white, colorless; also blue, green, brown, yellow, pink, violet
Crystal habitPrismatic, tabular, massive
CleavagePerfect on (001)
FractureUneven
Mohs scale hardness4.5–5
LusterVitreous; pearly
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity2.3–2.4
Refractive index1.536
Birefringence0.000–0.003
PleochroismDichroic (colorless)
Other characteristics Radioactive 4.37% (K)
References[2][3]

The name apophyllite refers to a specific group of phyllosilicates, a class of minerals. Originally, the group name referred to a specific mineral,[4] but was redefined in 1978 to stand for a class of minerals of similar chemical makeup that comprise a solid solution series, and includes the members fluorapophyllite-(K), fluorapophyllite-(Na), hydroxyapophyllite-(K). The name apophyllite is derived from the Greek apophyllízo (ἀποφυλλίζω), meaning 'it flakes off', a reference to this class's tendency to flake apart when heated, due to water loss. Exfoliation of apophyllite is also possible by treating it with acids or simply by rubbing it. These minerals are typically found as secondary minerals in vesicles in basalt or other volcanic rocks. A recent change (2008) in the nomenclature system used for this group was approved by the International Mineralogical Association, removing the prefixes from the species names and using suffixes to designate the species.[5] A subsequent nomenclature change approved by the International Mineralogical Association in 2013 renamed the minerals to include both suffixes and prefixes, as shown above.[6]

Though relatively unfamiliar to the general public, apophyllites are fairly prevalent around the world, with specimens coming from some of the world's most well-known mineral localities. These localities include: Jalgaon, India; the Harz Mountains of Germany, Mont Saint-Hilaire in Canada, and Kongsberg, Norway, with other locations in Scotland, Ireland, Brazil, Japan, and throughout the United States.

Structure

Apophyllite has an unusual structure for a phyllosilicate. Whereas most phyllosilicates have a T layer (silica backbone) consisting of interlocked 6-fold rings of silica tetrahedra, with pseudohexagonal symmetry, the T layer in apophyllite consists of interlocked 4-fold and 8-fold rings of silica tetrahedra with true tetragonal symmetry.[7][8]

  • T layer (silica backbone layer) of apophyllite
    T layer (silica backbone layer) of apophyllite
  • Structure of apophyllite viewed in the {100} direction, parallel to layering
    Structure of apophyllite viewed in the {100} direction, parallel to layering
  • Unit cell of apophyllite
    Unit cell of apophyllite

Species

  • Fluorapophyllite-(K) (formerly fluorapophyllite, apophyllite-(KF)), KCa4Si8O20(F,OH)·8H2O – white, colorless, yellow, green, violet[9]
  • Hydroxyapophyllite-(K) (formerly hydroxyapophyllite, apophyllite-(KOH)), KCa4Si8O20(OH,F)·8H2O – white, colorless[10]
  • Fluorapophyllite-(Na) (formerly natroapophyllite, apophyllite-(NaF)), NaCa4Si8O20F·8H2O – brown, yellow, colorless[11]
  • Fluorapophyllit-(Cs) (new) CsCa4(Si8O20)F·8H2O[12]
  • Fluorapophyllit-(NH4) (new) NH4Ca4(Si8O20)F⋅8H2O[13]
  • Isolated Fluorapophyllite-(K) cluster on contrasting matrix
    Isolated Fluorapophyllite-(K) cluster on contrasting matrix
  • Hydroxyapophyllite
    Hydroxyapophyllite
  • Fluorapophyllite-(Na)
    Fluorapophyllite-(Na)

See also

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. ^ "Radioactive Gems: ClassicGems.net".
  3. ^ Apophyllite data on Webmineral
  4. ^ Spencer 1911.
  5. ^ Burke, E.A.J. (2008): Tidying up mineral names: an IMA-CNMNC scheme for suffixes, hyphens and diacritical marks. Mineral. Rec., 39, 131–135.[1]
  6. ^ Hatert, Frederic; Mills, Stuart J.; Pasero, Marco; Williams, Peter A. (2013). "CNMNC guidelines for the use of suffixes and prefixes in mineral nomenclature, and for the preservation of historical names" (PDF). European Journal of Mineralogy. 25 (1): 113–115. Bibcode:2013EJMin..25..113H. doi:10.1127/0935-1221/2013/0025-2267. hdl:2268/136406.
  7. ^ Klein, Cornelis; Hurlbut, Cornelius S. Jr. (1993). Manual of mineralogy: (after James D. Dana) (21st ed.). New York: Wiley. pp. 522–523. ISBN 047157452X.
  8. ^ Ståhl, Kenny (1 January 1993). "A neutron powder diffraction study of partially dehydrated fluorapophyllite, KCa4Si8O20F.6.9H2O". European Journal of Mineralogy. 5 (5): 845–850. Bibcode:1993EJMin...5..845S. doi:10.1127/ejm/5/5/0845.
  9. ^ Apophyllite-(KF) on Mindat
  10. ^ Apophyllite-(KOH) on Mindat
  11. ^ Apophyllite-(NaF) on Mindat
  12. ^ Atali A. Agakhanov, Leonid A. Pautov, Anatoly V. Kasatkin, Vladimir Yu. Karpenko, Elena Sokolova, Maxwell C. Day, Frank C. Hawthorne, Vyacheslav A. Muftakhov, Igor V. Pekov, Fernando Cámara, Sergey N. Britvin (2019), "Fluorapophyllite-(Cs), CsCa4(Si8O20)F(H2O)8, a new apophyllite-group mineral from the Darai-Pioz Massif, Tien-Shan, northern Tajikistan", The Canadian Mineralogist (in German), vol. 57, no. 6, pp. 965–971, Bibcode:2019CaMin..57..965A, doi:10.3749/canmin.1900038, hdl:2434/681913, S2CID 210259462{{citation}}: CS1 maint: multiple names: authors list (link)
  13. ^ Martin Števko, Jiří Sejkora, Jakub Plášil, Zdeněk Dolníček, Radek Škoda (2020), "Fluorapophyllite-(NH4), NH4Ca4(Si8O20)F⋅8H2O, a new member of the apophyllite group from the Vechec quarry, eastern Slovakia", Mineralogical Magazine (in German), vol. 84, no. 4, pp. 533–539, Bibcode:2020MinM...84..533S, doi:10.1180/mgm.2020.44, S2CID 225484232, retrieved 2021-04-11{{citation}}: CS1 maint: multiple names: authors list (link), Format: PDF, KBytes: 623
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