The new mineral fluorbarytolamprophyllite, (Ba,Sr,K)2[(Na,Fe2+)3TiF2][Ti2(Si2O7)2O2] and chemical evolution of lamprophyllite-group minerals in agpaitic syenites of the Kola Peninsula

Refinement of the crystal structure of fresnoite, Ba2TiSi2O8, from Löhley (Eifel district, Germany); Gladstone–Dale compatibility, electronic polarizability and vibrational spectroscopy of minerals and inorganic compounds with pentacoordinated TiIVand a titanyl bond

“…Poor GD compatibility 1 À (K P /K c ) between chemical composition, refractive indices and density (Mandarino, 1981) is typical for titanium silicates with layered structures and nonequivalent Ti-O bonds. For example, for lamprophyllitegroup minerals the compatibility index is typically close to 0.11 (Chukanov et al, 2011a(Chukanov et al, , 2012(Chukanov et al, , 2014Filina et al, 2019). The GD compatibility indices of Ti-bearing micas, orlovite K(Li 2 Ti)-(Si 4 O 10 )OF (Sokolova et al, 2018) and oxyphlogopite K(Mg 2 Ti)(Si 3 AlO 10 )O 2 (Chukanov et al, 2011b(Chukanov et al, , 2019 in which Ti has sixfold coordination and occupies distorted octahedra exceed 0.06.…”

Crystal chemistry of lamprophyllite-group minerals from the Murun alkaline complex (Russia) and pegmatites of Rocky Boy and Gordon Butte (USA): single crystal X-ray diffraction and Raman spectroscopy study

“…The main specific structural features that characterize the lamprophyllite-type minerals are: fivefold coordination of the L cations in the H sheet and the absence of intermodular water molecules and/or complex anions such as (PO 4 ) 3À , (SO 4 ) 2À or (CO 3 ) 2À . The following eight mineral species are characterized by this type of the crystal structure: lamprophyllite (Krivovichev et al, 2003), fluorlamprophyllite (Andrade et al, 2018), barytolamprophyllite (Sokolova & Camara, 2008), fluorbarytolamprophyllite (Filina et al, 2019), lileyite (Chukanov et al, 2012), emmerichite (Aksenov et al, 2014;Chukanov et al, 2014), ericssonite (Moore, 1971) and ferroericssonite (Kampf et al, 2011). Schü llerite Sokolova et al, 2013) is not isotypic to lamprophyllite but has the same general crystal chemical formula and meets all above-listed criteria that define the lamprophyllite-type structure.…”

“…Minerals with the lamprophyllite-type structure are common components of different kinds of intrusive and effusive alkaline igneous rocks, related pegmatites and pneu-matolytic assemblages (Rastsvetaeva et al, 2016;Akimenko et al, 2015;Filina et al, 2019). According to the nomenclature approved by the Commission of New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association (IMA), lamprophyllite and isostructural titanium minerals are included in the seidozerite supergroup together with some chemically related titanium silicates (Sokolova & Cá mara, 2017).…”