Meionite Explained

Meionite
Category:Tectosilicate
Scapolite group
Formula:Ca4Al6Si6O24CO3
Imasymbol:Me[1]
Strunz:9.FB.15
System:Tetragonal
Class:Dipyramidal (4/m)
(same H-M symbol)
Symmetry:I4/m
Unit Cell:a = 12.179(1) Å,
c = 7.571(1) Å, Z = 2
Color:Colorless, white, grey, pink, violet, blue, yellow, orange-brown, brown
Cleavage:Distinct/good on
Fracture:Irregular/uneven, conchoidal
Tenacity:Brittle
Mohs:5–6
Luster:Vitreous, resinous, pearly
Streak:White
Diaphaneity:Transparent, opaque
Gravity:2.74–2.78
Opticalprop:Uniaxial (−)
Refractive:1.556 to 1.600
Birefringence:0.024 to 0.037
References:[2] [3] [4] [5]

Meionite is a tectosilicate belonging to the scapolite group with the formula Ca4Al6Si6O24CO3.[6] Some samples may also contain a sulfate group. It was first discovered in 1801 on Mt Somma, Vesuvius, Italy. It was named by Rene Just Haüy after μειωυ, the Greek word for less, in reference to the less acute pyramidal form as compared to vesuvianite.

As an end-member of the scapolite solid solution, meionite has the largest cell dimension [7] and very high thermal stability at high pressures. This indicates that meionite is one of the primary minerals in deep seated basic or intermediate magmatic processes. Meionite also breaks down to grossularite + kyanite + quartz + calcite at high pressure, similar to the upper pressure limits of anorthite. This sets its occurrence to the crustal rocks.[8]

Notes and References

  1. Warr. L.N.. 2021. IMA–CNMNC approved mineral symbols. Mineralogical Magazine. 85. 3. 291–320. 10.1180/mgm.2021.43. 2021MinM...85..291W. 235729616. free.
  2. https://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Meionite Mineralienatlas
  3. http://www.mindat.org/min-2627.html Mindat.org
  4. http://www.webmineral.com/data/Meionite.shtml Webmineral.com
  5. http://www.handbookofmineralogy.com/pdfs/meionite.pdf Handbook of Mineralogy
  6. Teertstra. David K.. Sherriff. Barbara L.. 1997-04-25. Substitutional mechanisms, compositional trends and the end-member formulae of scapolite. Chemical Geology. en. 136. 3. 233–260. 10.1016/S0009-2541(96)00146-5. 1997ChGeo.136..233T. 0009-2541.
  7. Eugster . Hans P. . Prostka . Harold J. . Appleman . Daniel E. . Unit-Cell Dimensions of Natural and Synthetic Scapolites . Science . 14 September 1962 . 137 . 3533 . 853–854 . 10.1126/science.137.3533.853. 17787337 . 2289057 .
  8. Newton . Robert C. . Goldsmith . Julian R. . Stability of the scapolite meionite (3CaAl2Si2O2 · CaCO3) at high pressures and storage of CO2 in the deep crust . Contributions to Mineralogy and Petrology . 1975 . 49 . 1 . 49–62 . 10.1007/BF00371078. 129389988 .