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Dollaseite-(Ce)
Dollaseite-(Ce) is a sorosilicate end-member epidote mineral and was discovered by Gajer (1927) in the Ostanmossa mine, Norberg district, Sweden, the mineral wrongly named “magnesium orthite” after Gajer (1927) himself was renamed after the structure refinement made to the mineral by Peacor and Dunn (1988) led to the proper classification. The name dollaseite-(Ce) was chosen in honor of Professor Wayne Dollase who performed broad research on the epidote-group minerals. The original confusion of the mineral’s composition was because of a complex atomic composition where an exchange of cations leads to a form of dollaseite-(Ce) that at first glimpse resembles an Mg analogue of allanite, now known as dissakisite-(Ce). Dollaseite-(Ce), although not very well known is part of a broad group of minerals, the epidote group which are primarily silicates, the most abundant type of minerals on earth. Dollaseite-(Ce) forms as dark-brown subhedral crystals primarily in Sweden mines. With the ideal chemical formula, CaREE3+Mg2AlSi3O11,(OH)F, dollaseite-(Ce) can be partially identified by its rare content of the REE(rare earth element) Ce.
==Composition==
With a general formula for the epidote group of A2M3Si3O13H〔Dollase, W.A. (1971) Refinement of the crystal structures of Epidote, Allanite and Hancockite. American Mineralogist, 56, 447-464〕 dollaseite-(Ce) receives its formula of CaREE3+Mg2AlSi3O11,(OH)F based on data from electron-microprobe analytical procedures. The results give the empirical formula (Ca.91 Ce.45 La.20 Nd.20 Pr.09 Sm.08 Gd.06)(Mg1.81 Fe.25)Al.97 Si3.0(OH)1.25 F.88 O10.99 from which the standard formula is then derived after applying Levinson’s rules for renaming REE minerals.〔Peacor, D.R. and Dunn P.J. (1988) Dollaseite-(Ce)(magnesium orthite redefined): Structure refinement and implications for F + M2+ substitutions in epidote-group minerals, American Mineralogist, 73, 838-842〕 Before any of these highly technological analyses were performed on dollaseite-(Ce) specimens, mistakes were made on the composition of the mineral. After further analysis were made it was determined that dollaseite-(Ce) was not the Magnesium (Mg) analogue of allanite as originally believed by Gaijer (1927) and was renamed. Geijer (1927) however, was not the only one to have had reported minerals with compositions that would be similar to an Mg analogue of allanite. Enami and Zang’s (1988), Meyer (1911), Hanson and Pearce (1941) also reported minerals that resembled the composition of an Mg analogue of allanite but none had sufficient data, or exact composition to be declared as an Mg analogue of allanite. It was not until 1991 that Edward S. Grew established dissakisite as the actual Mg dominant allanite mineral with formula Ca(Ce,La)MgAl2Si3O12(OH).〔Grew, E.S., Essene, E.J., Peacor D.R., Su, S. and Asami, M. (1991) Dissakisite-(Ce), a new member of the epidote group and the Mg analogue of allanite-(Ce), from Antarctica, American Mineralogist, 76, 1990-1997〕
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