Eudialyte group

Eudialyte group is a group of complex trigonal zircono- and, more rarely, titanosilicate minerals with general formula [N(1)N(2)N(3)N(4)N(5)]₃[M(1a)M(1b)]₃M(2)₃M(4)Z₃[Si₂₄O₇₂]O'₄X₂, where N(1) and N(2) and N(3) and N(5) = Na⁺ and more rarely H₃O⁺ or H₂O, N(4) = Na⁺, Sr²⁺, Mn²⁺ and more rarely H₃O⁺ or H₂O or K⁺ or Ca²⁺ or REE³⁺ (rare earth elements), M(1) and M(1b) = Ca²⁺, M(1a) = Ca²⁺ or Mn²⁺ or Fe²⁺, M(2) = Fe (both II and III), Mn and rarely Na⁺, K⁺ or Zr⁴⁺, M(3) = Si, Nb and rarely W, Ti and [] (vacancy), M(4) = Si and or rarely [], Z Zr⁴⁺ and or rarely Ti⁴⁺, and X = OH^−, Cl^− and more rarely CO₃^{2−} or F^−. Some of the eudialyte-like structures can even be more complex, however, in general, its typical feature is the presence of [Si₃O₉]^{6−} and [Si₉O₂₇]^{18−} ring silicate groups. Space group is usually R3m or R-3m but may be reduced to R3 due to cation ordering. Like other zirconosilicates, the eudialyte group minerals possess alkaline ion-exchange properties, as microporous materials.

List of the eudialyte-group minerals

Approved species

• Alluaivite - (space group R-3m)
• Andrianovite - (space group R3m)
• Aqualite – (space group R3)
• Carbokentbrooksite – (space group R3m)
• Davinciite – (space group R3m)
• Dualite – (space group R3m)
• Eudialyte – (space group R-3m)
• Feklichevite – (space group R3m)
• Fengchengite – (space group R-3m)
• Ferrokentbrooksite – (space group R3m)
• Georgbarsanovite – (space group R3m)
• Golyshevite – (space group R3m)
• Ikranite – (space group R3m)
• Ilyukhinite – – the most recent add (space group R3m)
• Johnsenite-(Ce) – (space group R3m)
• Kentbrooksite – (space group R3m)
• Khomyakovite – (space group R3m)
• Labyrinthite – (space group R3)
• Manganokhomyakovite – (space group R3m)
• Manganoeudialyte – (space group R3m)
• Mogovidite – (space group R3m)
• Oneillite – (space group R3)
• Raslakite – (space group R3)
• Rastsvetaevite – (space group R3m)
• Taseqite – (space group R3m)
• Voronkovite – (space group R3)
• Zirsilite-(Ce) – (space group R3m)

Unnamed species

The list of eudialyte-related natural phases is growing. There are many such phases, some of them very complex, coded "UM" by the International Mineralogical Association, and include:

• UM-1971-22-SiO:CaClFeHMgMnNaNbZr – – with variable substitution of OH for oxygen
• UM1990-79-SiO:CaClFeHMnNaNbREEZr – – first representative with magnesium-dominant site
• UM1990-80- SiO:CaFeHMnNaNbREEZr –
• UM1998-21-SiO:CaCeClHMnNaZr –
• UM1999-36-SiO:CaCeHMnNaNbSrZr –
• UM2000-66-SiO:CaClFeHMnNaNbSrZr –
• UM2003-39- SiO:CaClFeHHfNaNbSrTaTiZr –
• UM2004-51-SiO:CaClFFeHNaNbTi' –
• UM2006-17-SiO:CaClFFeHMnNaZr –
• UM2006-18-SiO:CaClFFeHMnNaZr – – with essential sulfur and with Zr dominant in two sites
• UM2006-28-SiO:CaHMnNaZr – – with double c unit cell dimension

In addition, there is "eudialyte 3248": , plus admixtures of Ce, Sr, Ba and Y, characterized by one S-dominant site (not shown in the simplified formula)

Other species

Rastsvetaeva et al. (2015) describe a species tentatively called "hydrorastsvetaevite", with a formula .

Further reading

• Rastsvetaeva, R. K.; Chukanov, N. V.; Zaitsev, V. A.; Aksenov, S. M.; Viktorova, K. A. (2018–05). "Crystal Structure of Cl-Deficient Analogue of Taseqite from Odikhincha Massif". Crystallography Reports. 63 (3): 349–357. doi:10.1134/s1063774518030240. ISSN 1063-7745

References

External links

• Mindat.org
• The Eudialyte homepage