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Niobian rutile from Haverstad and an unspecified locality in central Iveland, southern Norway, displays a novel two-stage exsolution of phase E, corresponding to titanian (Sc,Fe 3+ )(Nb>Ta)O 4 , not yet characterized as a mineral species. In general, rutile retains Ti, Fe 3+ (relative to Fe 2+ ), ∑Fe (relative to Mn) and Ta (relative to Nb), whereas the exsolved phase E concentrates Nb, Ta, ∑Fe, Sc, W, Zr, Mg and U. In the first stage, phase E forms platelets averaging ~20 × 2 μm; their orientation is controlled by the structure of the host rutile. The platelets contain ≤30.40 wt.% TiO 2 and Sc 2 O 3 as low as 3.37 wt.%, whereas the rutile retains ≤24.00 wt.% Nb 2 O 5 , ≤8.15 wt.% Ta 2 O 5 and ≤1.61 wt.% Sc 2 O 3 . In the second stage, coarsening of phase E produces irregular subround blebs 10 to 30 μm in size. Exsolution is advanced during this stage, increasing the Sc content of phase E up to 10.06 wt.% Sc 2 O 3 and reducing its Ti content to as low as 11.90 wt.% TiO 2 , whereas the rutile matrix is depleted in Nb, Ta and Sc to as low as 21.30, 7.61 and 0.52 wt.% of the respective oxides. The average Fe 3+ :Fe 2+ ratio of rutile is 3.51, whereas it decreases to 3.18 in platelets of phase E, and it drops to 2.60 in the blebs of the second-generation phase E. The platelet stage might prove to be typical of exsolution of phase E from niobian rutile with high (Sc,Fe) 3+ /Fe 2+ , in contrast to the much more widespread granular exsolution of titanian ixiolite or titanian ferrocolumbite from Sc-poor niobian rutile with Fe 3+ /Fe 2+ much less than 1.

TWO-STAGE EXSOLUTION OF A TITANIAN (Sc,Fe3+)(Nb,Ta)O4 PHASE IN NIOBIAN RUTILE FROM SOUTHERN NORWAY