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{{short description|Phyllosilicate mineral}}

factoids

| molweight = | color = Usually white, colorless; also blue, green, brown, yellow, pink, violet| habit = Prismatic, tabular, massive| system = Tetragonal| symmetry = P4/mnc| twinning = | cleavage = Perfect on (001)| fracture = Uneven| mohs = 4.5–5| luster = Vitreous; pearly| refractive = 1.536| opticalprop = | birefringence = 0.000–0.003| pleochroism = Dichroic (colorless)| streak = White| gravity = 2.3–2.4| melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Transparent to translucentImage:Radioactive.svg>25px Radioactive 4.37% (K) Apophyllite data on Webmineral}}The name apophyllite refers to a specific group of phyllosilicates, a class of minerals. Originally, the group name referred to a specific mineral,{{sfn|Spencer|1911}} 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 {{transl|grc|apophyllízo}} ({{wikt-lang|grc|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.Burke, E.A.J. (2008): Tidying up mineral names: an IMA-CNMNC scheme for suffixes, hyphens and diacritical marks. Mineral. Rec., 39, 131–135.weblink A subsequent nomenclature change approved by the International Mineralogical Association in 2013 renamed the minerals to include both suffixes and prefixes, as shown above.JOURNAL, 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,weblink European Journal of Mineralogy, 25, 1, 113–115, 10.1127/0935-1221/2013/0025-2267, 2013EJMin..25..113H, 2268/136406, 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.BOOK, Klein, Cornelis, Hurlbut, Cornelius S. Jr., Manual of mineralogy: (after James D. Dana), 1993, Wiley, New York, 047157452X, 21st, 522–523, JOURNAL, Ståhl, Kenny, A neutron powder diffraction study of partially dehydrated fluorapophyllite, KCa4Si8O20F.6.9H2O, European Journal of Mineralogy, 1 January 1993, 5, 5, 845–850, 10.1127/ejm/5/5/0845, 1993EJMin...5..845S, File:Apophyllite T.png|T layer (silica backbone layer) of apophylliteFile:Apophyllite 100.png|Structure of apophyllite viewed in the {100} direction, parallel to layeringFile:Apophyllite unit cell.png|Unit cell of apophyllite

Species

• Fluorapophyllite-(K) (formerly fluorapophyllite, apophyllite-(KF)), KCa4Si8O20(F,OH)·8H2O – white, colorless, yellow, green, violetApophyllite-(KF) on Mindat
• Hydroxyapophyllite-(K) (formerly hydroxyapophyllite, apophyllite-(KOH)), KCa4Si8O20(OH,F)·8H2O – white, colorlessApophyllite-(KOH) on Mindat
• Fluorapophyllite-(Na) (formerly natroapophyllite, apophyllite-(NaF)), NaCa4Si8O20F·8H2O – brown, yellow, colorlessApophyllite-(NaF) on Mindat
• Fluorapophyllit-(Cs) (new) CsCa4(Si8O20)F·8H2O

{{citation|surname1=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|periodical=The Canadian Mineralogist|title=Fluorapophyllite-(Cs), CsCa4(Si8O20)F(H2O)8, a new apophyllite-group mineral from the Darai-Pioz Massif, Tien-Shan, northern Tajikistan|volume=57|issue=6|at=pp. 965–971|date=2019|language=German|doi=10.3749/canmin.1900038hdl=2434/681913hdl-access=free}}

• Fluorapophyllit-(NH4) (new) NH4Ca4(Si8O20)Fâ‹…8H2O

{{citation|surname1=Martin Å tevko, Jiří Sejkora, Jakub Plášil, ZdenÄ›k Dolníček, Radek Å koda|periodical=Mineralogical Magazine|title=Fluorapophyllite-(NH4), NH4Ca4(Si8O20)Fâ‹…8H2O, a new member of the apophyllite group from the Vechec quarry, eastern Slovakia|volume=84|issue=4|at=pp. 533–539|date=2020|language=German|doi=10.1180/mgm.2020.44|bibcode=2020MinM...84..533S |s2cid=225484232 |url=https://www.researchgate.net/publication/341800393|access-date=2021-04-11}}, Format: PDF, KBytes: 623Apophyllite-(KF)-66684.jpg|Isolated Fluorapophyllite-(K) cluster on contrasting matrixHydroxyapophyllite on white background.jpg|HydroxyapophylliteNatroapophyllite-ind11b.jpg|Fluorapophyllite-(Na)

See also

• Carbonatite
• Gyrolite
• Zeolite
• List of minerals

References

{{reflist}}

• MinDat Listing
• weblink" title="web.archive.org/web/20051029140604weblink">Mineral Galleries
• JOURNAL, Colville AA, Anderson CP, Black PM, Refinement of the crystal structure of apophyllite: I. X-ray diffraction and physical properties, American Mineralogist, 1971, 56, 1222–1233,
• EB1911, Apophyllite, 2, 195, Leonard James, Spencer, Leonard James Spencer, This describes the older definition as a specific mineral.

{{Commons category|Apophyllite}}