2007 ÇÀÏÈÑÊÈ ÐÎÑÑÈÉÑÊÎÃÎ ÌÈÍÅÐÀËÎÃÈ×ÅÑÊÎÃÎ ÎÁÙÅÑÒÂÀ ×. CXXXVI, ¹ 4 2007 ZAPISKI RMO (PROCEEDINGS OFTHE RUSSIAN MINERALOGICAL SOCIETY) Pt CXXXVI, N 4 ÍÎÂÛÅ ÌÈÍÅÐÀËÛ ÓÄÊ 549.6 © Ïî÷åòíûé ÷ë. À. Ï. ÕÎÌßÊÎÂ,* ä. ÷ë. Ã. Í. ÍÅ×ÅËÞÑÒÎÂ,** ä. ÷ë. Ð. Ê. ÐÀÑÖÂÅÒÀÅÂÀ*** ÄÓÀËÈÒ Na30(Ca,Na,Ce,Sr)12(Na,Mn,Fe,Ti)6Zr3Ti3MnSi51O144(OH,H2O,Cl)9 — ÍÎÂÛÉ ÖÈÐÊÎÍÎ-ÒÈÒÀÍÎÑÈËÈÊÀÒ Ñ ÌÎÄÓËßÐÍÎÉ ÝÂÄÈÀËÈÒÎÏÎÄÎÁÍÎÉ ÑÒÐÓÊÒÓÐÎÉ ÈÇ ËÎÂÎÇÅÐÑÊÎÃÎ ÙÅËÎ×ÍÎÃÎ ÌÀÑÑÈÂÀ, ÊÎËÜÑÊÈÉ ÏÎËÓÎÑÒÐÎÂ, ÐÎÑÑÈß1 A. P. KHOMYAKOV, G. N. NECHELYUSTOV, R. K. RASTSVETAEVA. DUALITE, Na30(Ca,Na,Ce,Sr)12(Na,Mn,Fe,Ti)6Zr3Ti3MnSi51O144(OH,H2O,Cl)9, A NEW ZIRCONO-TITANOSILICATE WITH A MODULAR EUDIALYTE-LIKE STRUCTURE FROM LOVOZERO ALKALINE MASSIF, KOLA PENINSULA, RUSSIA * Èíñòèòóò ìèíåðàëîãèè, ãåîõèìèè è êðèñòàëëîõèìèè ðåäêèõ ýëåìåíòîâ, 121357, Ìîñêâà, óë. Âåðåñàåâà, 15; e-mail: [email protected] ** Âñåðîññèéñêèé íàó÷íî-èññëåäîâàòåëüñêèé èíñòèòóò ìèíåðàëüíîãî ñûðüÿ, 109017, Ìîñêâà, Ñòàðîìîíåòíûé ïåð., 31 *** Èíñòèòóò êðèñòàëëîãðàôèè ÐÀÍ, 117333, Ìîñêâà, Ëåíèíñêèé ïð., 59 Dualite was found on Mt. Alluaiv (Lovozero massif, Kola Peninsula), in hyperagpaitic pegmatoid rock as rare anhedral grains up to 0.3—0.5 mm across. Associated minerals are: sodium-potassium feldspar, nepheline, sodali- te, cancrinite, aegirine, alkaline amphibole, eudialyte, lovozerite, lomonosovite, vuonnemite, lamprophyllite, spha- lerite and villiaumite. It is yellow, transparent or translucent, with conchoidal fracture; brittle; luster vitreous; streak white. Mohs’ hardness 5. D(meas.) = 2.84(3) g/cm3 (volumetric method), D(calc.) = 2.814 g/cm3. The mineral dis- solves and gelatinises in acid at room temperature. Non-fluorescent. Optically uniaxial, positive, no = 1.610(1), 3 ne = 1.613(1). Trigonal, space group R3m, a = 14.153(9), c = 60.72(5) Å, V = 10533(22) Å , Z = 3. The strongest lines of the powder diffraction pattern [d, Å(I)(hkl)] are: 7.11(40)(110), 4.31(50)(0.2.10), 2.964(100)(1.3.10), 2.839(90)(048), 2.159(60)(2.4.10, 0.4.20), 1.770(60)(2.4.22, 4.0.28, 440), 1.362(50) (5.5.12, 3.0.42). Chemical composition (wt. %, electron probe, H2O content from crystal structure analysis): Na2O 17.74, K2O 0.08, CaO 8.03, SrO 1.37, BaO 0.29, MnO 2.58, FeO 1.04, La2O3 0.79, Ce2O3 1.84, Nd2O3 0.88, Al2O3 0.20, SiO2 51.26, TiO2 4.40, ZrO2 5.39, Nb2O5 1.94, Cl 0.58, H2O 1.39, –O = Cl2 0.13, ñóììà 99.67. Empirical formula (based on Ócations = = 106 apfu as determined by crystal structure analysis) is (Na29.79Ba0.1K0.10)Ó30 (Ca8.55Na1.39REE1.27Sr0.79)Ó12$ 2+ $ (Na3.01 Mn1.35 Fe087. Ti 077. )S6 (Zr2.61Nb0.39)Ó3 (Ti2.52Nb0.48)S3 (Mn0.82Si0.18)S1 (Si50.77Al0.23)Ó51 O144[(OH)6.54(H2O)1.34 Cl0.98]Ó8.86. Simplified formula: Na30(Ca,Na,Ce,Sr)12(Na,Mn,Fe,Ti)6Zr3Ti3 MnSi51O144(OH,H2O,Cl)9. The name dualite is derived from the Latin «dualis» [dual] in allusion to the dual taxonomic membership of the mineral, which is at once a zirconosilicate and titanosilicate. The crystal structure is characterized by the presence of two types of modules (alluivite-like and eudialyte-like) alternating along the triad axis, causing dualite to have a double c period relative to eudialyte and a close crystal chemical relationship to rastsvetaevite (ZRMO, 2006, N 1) and labyrynthite (ZRMO, 2006, N 2). According to the authors’ crystal chemical systematics of the eudialyte group, the mineral be- longs to one of its three principal subgroups characterized by a 24-layered structural array. Dualite is a late-pegmati- tic mineral formed during the final stages of hyperagpaitic pegmatite formation. Type material is deposited at the Fersman Mineralogical Museum, Moscow. Êàê èçâåñòíî, íåñìîòðÿ íà áîëüøóþ áëèçîñòü èîííûõ ðàäèóñîâ è õèìè÷åñêèõ ñâîéñòâ òèòàíà è öèðêîíèÿ, ýòèì ýëåìåíòàì ïðèñóùè ãëóáîêèå ðàçëè÷èÿ êðèñòàëëî- õèìè÷åñêèõ ôóíêöèé, îñîáåííî ðåçêî ïðîÿâëÿþùèåñÿ â ñòðåìëåíèè Ti-îêòàýäðîâ ê 1 Ìèíåðàë è åãî íàçâàíèå óòâåðæäåíû ÊÍÌÍÌ ÌÌÀ 8 èþëÿ 2005 ã. 31.