Status of olgite and bario-olgite


E.A.J. Burke, chairman IMA-CNMNC


It is stated, in several media, that bario-olgite, approved by the IMA-CNMMN as 2003-002 and published by Pekov et al. (2004), has been discredited, or should be discredited as a valid mineral. These opinions are based on the conclusion by Sokolova et al. (2005) that “bario-olgite is not distinct from olgite, the former should be considered for discreditation�. This consideration became reality when Sokolova and Hawthorne submitted in 2005, on invitation of the IMA-CNMMN, an official proposal to discredit bario-olgite. In the period from January to May 2006, this proposal was intensely discussed, guided by Giovanni Ferraris as vice-chairman of the CNMMN, between its authors, the authors of bario-olgite and the members of the CNMMN.


The history of olgite and bario-olgite is as follows:

1. Until 2004, olgite was considered in all mineralogical reference books to be a strontium mineral, due to the formula given in the original description by Khomyakov et al. (1980), Na(Sr,Ba)PO4, and to the composition of the M1 structural site as obtained by Sokolova et al. (1984), (Sr0.52Ba0.48), on type material from Mt. Karnasurt, Lovozero massif, Kola Peninsula, Russia.

2. Sokolova et al. (1990) published data on ‘olgite II’ and ‘olgite III’ (the original olgite being ‘olgite I’), two specimens from Mt. Alluaiv in the Lovozero massif having Ba as dominant constituent on the M1 site. This paper failed to give a clear definition of olgite, no nomenclatural distinction was made between the 1984 olgite (Sr-dominant M1) and the 1990 olgite (Ba-dominant M1).

3. Pekov et al. started in 2002 a study on ‘olgite’ specimens from several pegmatites and hydrothermal veins at Mt. Kedykverpakhk in the Lovozero massif. The results indicated that ‘olgite’ consists of two mineral species, with either Sr or Ba dominant on the M1 site. Because olgite was traditionally interpreted as a strontium mineral, Pekov et al. (2004) published their material with a Ba-dominant M1 site as the new mineral bario-olgite after approval by the CNMMN in 2003. It is evident that ‘olgite II’ and ‘olgite III’ are also bario-olgite. Pekov (2005) published data of an ‘olgite’ specimen from one of the veins having a Sr-dominant M1 composition of (Sr0.57Ba0.42K0.01).

4. Sokolova et al. (2005) re-examined the material described previously as ‘olgite I’ (= the original type material) and ‘olgite III’. They found that the real space group of these specimens is P-3m1, not P3 as published in 1984 and 1990 and also by Pekov et al. (2004) for bario-olgite. The change of space group has no implications for the occupancy of the M1 site, which is identical in both space groups. The new data obtained on the type ‘olgite I’ specimen, however, show that its M1 site has a composition (Ba0.76Sr0.20K0.04). Calculation of the empirical formula from the original analysis by Khomyakov et al. (1980) along the same crystal-chemical principles leads to essentially the same results. No convincing explanation was offered for the strong difference with the 1984 results (with a Sr-dominant M1 site) on the same specimen.


Giovanni Ferraris proposed in June 2006 the following compromise to end the discussion:

1. It is evident that ‘re-examined olgite’ and ‘bario-olgite’ represent the same mineral species.

2. According to the CNMMN rules, the older name (olgite) should have priority. But taking into account the work done by Pekov in 2005 showing that in the near future a ‘strontio-olgite’ will be described, as an exception (but that would not be the first time!) to the priority rule, the name ‘olgite’ is discredited and the name ‘bario-olgite’ is retained.

3. The samples studied by Pekov et al. (2004) and by Sokolova et al. (2005) are the cotypes of the redefined ‘bario-olgite’.


It was at that time also agreed between Ferraris, Pekov, Sokolova and Hawthorne that:

1. Sokolova and Hawthorne have withdrawn their proposal to discredit bario-olgite after reading the comments of the CNMMN members.

2. In the future, ‘olgite’ will be used as the name of a series consisting of the species ‘bario-olgite’ and ‘strontio-olgite’ after approval of the latter as a mineral.

3. Pekov et al. will at some moment submit a proposal for the Mt. Kedykverpakhk ‘strontio-olgite’ together with an official discreditation of the old ‘olgite’ and a revision of the formula of ‘bario-olgite’.


Conclusions in 2008:

1. The 2006 compromise and agreements are taken over by the CNMNC: bario-olgite is to be redefined, olgite is to be discredited as a mineral name and is to be used as a series name (comparable to the apatite, columbite, apophyllite, etc.), and ‘strontio-olgite’ is to be proposed as a new mineral. The authors of the latter are invited to consider renaming the minerals of the olgite series along a suffix-based nomenclature: olgite-(Ba) and olgite-(Sr). Until that time, the names bario-olgite and olgite, respectively, are to be used for these two minerals.

2. Sokolova et al. (2005) would have avoided a lot of confusion and discussion if they had contacted the authors of bario-olgite and/or the CNMMN before publishing their results.

3. Publication of the results of the 2006 discussion within the CNMMN is necessary to correct wrong statements in several media.


References


Khomyakov, A.P., Semenov, E.I., Shumyatskaya, N.G., Timoshenkov, I.M., Laputina, I.P., Smol’yaninova, N.N. (1980): Olgite, Na(Sr,Ba)PO4 - a new mineral. Zapiski VMO, 109, 3, 347-351 (in Russian).

Pekov, I.V. (2005): Genetic Mineralogy and Crystal Chemistry of Rare Elements in High-Alkaline Postmagmatic Systems. D.Sc. Thesis. Moscow State University, 652 pp.

Pekov, I.V., Chukanov, N.V., Kulikova, I.M., Zubkova, N.V., Krotova, O.D., Sorokina, N.I., Pushcharovsky, D.Yu. (2004): A new mineral bario-olgite and its crystal structure. Zapiski VMO, 133, 1, 41-49 (in Russian)

Sokolova, E.V., Egorov-Tismenko, Yu.K., Yamnova, N.A., Simonov, M.A. (1984): The crystal structure of olgite, Na(Sr0.52Ba0.48)(Sr0.58Na0.42)(Na0.81Sr0.19) . Kristallografiya, 29, 6, 1079-1083 (in Russian).

Sokolova, E.V., Nadezhina, T.N., Khomyakov, A.P. (1990): The X-ray study of high-barian olgite. Vestnik Moskovskogo Universiteta, ser. 4: Geology, No. 1, 87-91 (in Russian).

Sokolova, E., Hawthorne, F.C., Khomyakov, A.P. (2005): Refinement of the crystal structure and revision of the chemical formula of olgite: (Ba,Sr)(Na,Sr,REE)2Na2. Can. Mineral., 43, 1521-1526.