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A tantalum-rich variety of sphene N I o B I U M and tantalum have long been recognized as important minor constituents of sphenes. Since these elements have ionic radii of 0"69 and o.68/ ~ respectively their substitution for titanium (o-68 A) in the structure is not unexpected, but no reliable...
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.622.9004 http://www.minersoc.org/pages/Archive-MM/Volume_39/39-305-605.pdf |
| Summary: | A tantalum-rich variety of sphene N I o B I U M and tantalum have long been recognized as important minor constituents of sphenes. Since these elements have ionic radii of 0"69 and o.68/ ~ respectively their substitution for titanium (o-68 A) in the structure is not unexpected, but no reliable reports exist of sphenes containing more than 2 % (Nb2Os+Ta2Os). One of the highest concentrations of these lements was noted by Sahama (I946) in a large zoned sphene crystal from Nuolainniemi, Impilahti, Finland, the altered part of which contained 3"3 % Nb2Os and 2. 9 % Ta2Os. The crystal, however, contained numerous inclusions of a mineral thought to be wiikite, a metamict niobotantalate of Ti, the rare earths, Ca, and U, which casts some doubt on the analysis. A sphene from the Kola Peninsula has been reported by Burova (in Fersman and Bohnstedt, I937) as containing 1.87 % (Nb2Os-?Ta~Os). We have recently obtained further information on this subject during an examination of the type specimen of strtiverite (spec. no. BM. I9O6, I23). This strfiverite occurred as small black crystalline masses embedded in feldspar and quartz from the pegmatite |
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