Kolskyite, a new layered titanosilicate: inverse prediction.

Kolskyite, ideally (Ca)Na2Ti4(Si2O7)2O4(H2O)7, is a new mineral discovered in the Khibiny alakaline massif, Kola Peninsula, Russia (IMA2013-005). The mineral is named after Kola Peninsula (Kolskyi Poluostrov in Russian) and commemorates the outstanding achievements of Alexander P. Khomyakov, a prominent mineralogist who described more than 100 new minerals (primarily from Kola). This mineral has no natural or synthetic structural analogues. Kolskyite is a new TS-block mineral of Group IV (TS = titanium silicate) (Sokolova, 2006). There are two types of TS-block structures: basic and derivative structures. A derivative structure is related to a number of basic structures so we can predict derivative structures as combination of basic structures of the same group. Using inverse prediction, the basic crystal structure of kolskyite was predicted as a component of known derivative structures (Sokolova & Cámara, 2010). The crystal structure of kolskyite is of basic type, 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 , Z = 1, and is a combination of TS and I (intermediate) blocks. In kolskyite, the TS block has the stereochemistry and topology of Group IV where Ti + Nb = 4 apfu. In the crystal structure of kolskyite, TS and I blocks have following compositions: Na2Ti4(Si2O7)2O4(H2O)2 and [(Ca)(H2O)5], respectively.