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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

Bermanec, Vladimir ; Tomašić, Nenad ; Kniewald, Goran ; Back, Malcolm Properties and classification problem of a Nb- and Y-rich mineral of aeschynite mineral group // 18th General Meeting of the International Mineralogical Association - Programme with abstracts. Edinburgh: International Mineralogical Association, 2002. str. 121-122-x

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)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.

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

Povezanost rada

Geologija