| Summary: | Kazanskyite, ideally BaNa3Ti2Nb(Si2O7)2O2(OH)2(H2O)4, P-1, triclicnic: a 5.4260(9), b 7.135(1), c 25.514(4)Å, α 98.172(4), β 90.916(4), γ 89.964(3)º, V 977.61(5) Å3, Z = 2, is a new representative of titanium disilicate minerals with the TS (titanium silicate) block[1]. It occurs at Kirovskii mine, Mt. Kukisvumchorr, the Khibiny alkaline massif, Kola Peninsula (Russia), associated to natrolite, barytolamprophyllite, nechelyustovite, hydroxylapatite, belovite-(La), belovite-(Ce), gaidonnayite, nenadkevichite, epididymite, apophyllite-(KF), sphalerite. The crystal structure of kazanskyite is a new structure type and does not have any analogues. It is a combination of a TS block and an I (intermediate) block. The TS block consists of HOH sheets (H = heteropolyhedral, O = octahedral). The TS block exhibits linkage and stereochemistry typical for Group III (Ti+Nb = 3 a.p.f.u.) of the Ti-disilicate minerals: two H sheets connect to the O sheet such that two (Si2O7) groups link to the trans edges of a Ti octahedron of the O sheet [1]. In the O sheet, there are four MO sites. The MO(1) and MO(2), MO(3), MO(4) sites are occupied by Ti0.74Mn0.26 and Na, Na0.77Mn0.15Ca0.07Fe2+0.01, Na0.77Mn0.15Ca0.07Fe2+0.01, respectively. The cation composition of the O sheet is ideally Na3Ti p.f.u. (per formula unit). The TS block has two H sheets, H1 and H2, which differ in coordination number and dominant cation at the MH site, [6]-coordinated Nb and [5]-coordinated Ti, respectively. In the H sheets, there are four Si sites occupied solely by Si and tetrahedrally coordinated by O atoms, with <Si-O> = 1.62 Å. In the H sheet, (Si2O7) groups link to MH polyhedra. The chemical formulae of the H sheets is ideally NbTi(Si2O7)2(H2O) and of the TS block is Na3Ti2Nb(Si2O7)2O2(OH)2(H2O). There are two peripheral sites, AP (1) and AP(2), occupied by Ba0.51Sr0.28K0.21 and Ba0.19 0.81, respectively. There are two I blocks: the I1 block is a layer of AP(1) atoms with ideal composition Ba a.p.f.u.; the I2 block consists of AP(2) atoms and H2O ...
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