Naslov
Properties and classification problem of a Nb- and Y-rich mineral of aeschynite mineral group

Autori
Bermanec, Vladimir ; Tomašić, Nenad ; Kniewald, Goran ; Back, Malcolm

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
18th General Meeting of the International Mineralogical Association - Programme with abstracts / - Edinburgh : International Mineralogical Association, 2002, 121-122

Skup
18th General Meeting of the International Mineralogical Association

Mjesto i datum
Edinburgh, Ujedinjeno Kraljevstvo, 01.09.2002. - 06.09.2002

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
aeschynite; crystal-chemical properites; substitutions; mineral classification

Sažetak
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)Å, b = 10.983(5)Å, c = 7.467(4)Å, V = 433.8(3)Å3) 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.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

POVEZANOST RADA