Properties and classification problem of a Nb- and Y-rich mineral of aeschynite mineral group (CROSBI ID 483944)
Prilog sa skupa u zborniku | sažetak izlaganja sa skupa | međunarodna recenzija
Podaci o odgovornosti
Bermanec, Vladimir ; Tomašić, Nenad ; Kniewald, Goran ; Back, Malcolm
engleski
Properties and classification problem of a Nb- and Y-rich mineral of aeschynite mineral group
Complex oxides of Nb, Ta, Ti and REE frequently show a tendency for large scale cation substitution on certain atomic positions in crystal structure. The aeschynite mineral group with general formula AB2O6 is a typical representative of this phenomenon as cations are mutually interchanged on A and B sites of the crystal structure. REE3+, Ca2+ and Th4+ predominantly occupy site A while Ti4+, Nb5+ and Ta5+ occupy site B. The dominant substitution mechanism is Ca2+ + (Nb5+, Ta5+) <> REE3+ + Ti4+. This mechanism leads to an occurence of different mineral group members. The diffraction data of the investigated mineral sample originating from Bear Lake, Ontario, Canada, are closest to those of aeschynite mineral group being most similar to the mineral once called lyndochite. The comparison of its chemical data to those of aeschynite group minerals also shows a close similarity to previous findings of lyndochite and to niobo-aeschynites as well. The chemical composition also partly resembles euxenite. However, diffraction data with the most prominent peaks (intensities in parentheses) 3.088 (20), 3.018 (100) and 2.939 (69) are more common for aeschynite group minerals. This is also the case with the unit cell parameters (a = 5.290(4)&Aring;, b = 10.983(5)&Aring;, c = 7.467(4)&Aring;, V = 433.8(3)&Aring;3) having the values between those for niobo-aeschynite-(Ce) and aeschynite-(Y). The calculated chemical formula is (REE0.53Ca0.31Fe2+0.11Th0.18U0.009)(Nb0.95Ti0.92Ta0.07)O6. On site B Nb is dominant, thus the mineral is close to niobo-aeschynites. However, all known niobo-aeschynites have Ce or Nd as the dominant cation on site A while Y is the dominant cation in this case. In aeschynite group Y is dominant cation on position A in the case of aeschynite-(Y). So, the investigated mineral could be treated as a boundary case between aeschynite-(Y) and niobo-aeschynite.
aeschynite; crystal-chemical properites; substitutions; mineral classification
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Podaci o prilogu
121-122-x.
2002.
objavljeno
Podaci o matičnoj publikaciji
18th General Meeting of the International Mineralogical Association - Programme with abstracts
Edinburgh: International Mineralogical Association
Podaci o skupu
18th General Meeting of the International Mineralogical Association
poster
01.09.2002-06.09.2002
Edinburgh, Ujedinjeno Kraljevstvo