Paper No. 1
Presentation Time: 8:00 AM

KOLSKYITE, A NEW TS-BLOCK MINERAL: PREDICTION AND REALITY


SOKOLOVA, Elena1, CÁMARA, Fernando2, HAWTHORNE, Frank1 and KHOMYAKOV, Alexander3, (1)Geological Sciences, University of Manitoba, 125 Dysart Road, 240 Wallace Bldg, Winnipeg, MB R3T 2N2, Canada, (2)Dip. Scienze della Terra, Università degli Studi di Torino, Torino, I-10125, Italy, (3)(deceased), Institute of Mineralogy, Geochemistry and Crystal Chemistry of Rare Elements, Moscow, 121357, Russia, elena_sokolova@umanitoba.ca

Kolskyite, ideally (Ca◊)Na2Ti4(Si2O7)2O4(H2O)7 (◊=vacancy), is a new mineral discovered in the Khibiny alkaline massif, Kola Peninsula, Russia (IMA2013-005). Kolskyite is a new TS-block mineral (TS = titanium silicate) (Sokolova, 2006). The TS block consists of HOH sheets where H = heteropolyhedral and O = octahedral, and it is the main structural unit in the TS-block structures. There are four Groups of TS-block structures where Ti equals 1, 2, 3 and 4 apfu. The crystal structure of kolskyite belongs to Group IV where Ti = 4 apfu, a = 5.387(1), b = 7.091(1), c = 15.473(3) Å, α = 96.580(4), β = 93.948(4), γ = 89.818(4)o, V = 585.8(3) Å3, space group P-1 , Z = 1, and is a combination of TS and I (intermediate) blocks. In the crystal structure of kolskyite, TS and I blocks have following compositions: Na2Ti4(Si2O7)2O4(H2O)2 and [(Ca◊)(H2O)5], respectively.

The discovery of kolskyite is extremely important for us as it proves that we can predict crystal structures of TS-block minerals: the crystal structure of kolskyite was predicted by Sokolova & Cámara (2010). Sokolova & Cámara (2010) defined two types of TS-block structures: basic and derivative structures. A basic structure has only one type of TS block and only one type of I block; in a derivative structure, there is more than one type of TS block and there is more than one type of I block. A derivative structure is related to a number of basic structures of the same group. Hence we can predict a derivative structure as a combination of structural fragments of basic structures. Using inverse prediction, the basiccrystal structure of kolskyite was predicted as a component of known derivative structures.

References:

Sokolova, E. (2006) From structure topology to chemical composition: I. Structural hierarchy and stereochemistry in titanium disilicate minerals. Canadian Mineralogist, 44, 1273-1330.

Sokolova, E. & Cámara, F. (2010) From chemical composition to structure topology in Ti silicates. 20th General Meeting of the International Mineralogical Association, Abstracts, Budapest, Hungary.