We consider structure topology for a group of Ti disilicates based on our single-crystal X-ray structure work on four Tidisilicate minerals, jinshajiangite, cámaraite, bornemanite and nechelyustovite, and two possible new mineral species with preliminary ideal formulae Na4BaTi2Nb(Si2O7)2O3(OH) (H2O)2 (mineral A) and Na3KBaTi2Nb(Si2O7)2O3(OH)(H2O)6 (mineral B). These minerals belong to a group of Ti silicates with a TS (titanium silicate) block [1-4]. Structure types of cámaraite, bornemanite, nechelyustovite and minerals A and B are new. The general formula of the TS block is AP 2BP 2MH 2MO 4(Si2O7)2X4+n, where MH 2 and MO 4 are cations of the H and O sheets; MH = Ti, Nb, Zr, Mn2+, Ca; MO = Ti, Zr, Fe2+, Mn2+, Ca, Na; AP and BP = cations at the peripheral (P) sites = Na, Ca, Ba, K; X = O, OH, F; n = 0,2,4 [4]. The TS block is composed of a central trioctahedral (O) sheet and two adjacent (H) sheets of [5-7]-coordinated polyhedra and (Si2O7) groups. All structures consist of a TS block and an I (intermediate) block that comprises atoms between two TS blocks. The I block consists of alkali and alkaline-earth cations, (H2O) groups and the oxyanions (PO4), (SO4) and (CO3). Structures of Ti disilicate minerals have been divided into four groups, each characterized by different linkage, content and stereochemistry of Ti (= Ti+Nb) in the TS block. In Groups I, II, III and IV, Ti = 1, 2, 3 and 4 apfu, respectively [4] In jinshajiangite and cámaraite, Ti = 2 apfu and the TS block exhibits the stereochemistry of Group II. In bornemanite, nechelyustovite, minerals A and B, Ti = 3 apfu, the TS block is as in Group III. Jinshajiangite contains one type of I block (as in perraultite); cámaraite, bornemanite and minerals A and B, two types of I block; nechelyustovite, three topologically and chemically different I blocks. The structures of nechelyustovite and mineral B contain a new (for TS-block minerals) type of I block, an array of H2O groups of ideal composition (H2O)5. Structures with a new type of TS block (more than one I block and more than one type of self-linkage of TS blocks) are related to structures of other minerals from the same Group: cámaraite, to bafertisite and jinshajiangite (Group II); bornemanite, to vuonnemite and barytolamprophyllite (Group III); nechelyustovite, to epistolite, barytolamprophyllite and a yet unknown structure (Group III); mineral A, to epistolite and barytolamprophyllite (Group III); mineral B, to barytolamprophyllite and a yet unknown structure. Minerals with a new type of TS-block structure and related minerals occur in the same environment and often form intimate intrgrowths. Discovery of five minerals with a new type of a TS-block structure (a) confirms that the chemical composition of the I block dictates the type of self-linkage of TS blocks [5]; (b) emphasizes the role of Ba Na exchange which results in changes in the topology of the I block and subsequently selflinkage of TS blocks (e.g. the bafertisite-cámaraitejinshgagiangite series); (c) enlarges the number of transformation-mineral series [6] due to Na-depletion, bornemanite ! nechelyustovite, Group III. [1] Belov, N.V. (1976) Essays on Structural Mineralogy. Nedra, Moscow. [2] Pyatenko, Yu. A. et al. (1976) Mineralogical crystal chemistry of titanium. Nauka, Moscow. [3] Egorov-Tismenko, Yu.K. & Sokolova, E.V. (1990) Mineral. Zh., 12(4), 40-49 (in Russian). [4] Sokolova, E. (2006). Can. Mineral., 44, 1273-1330. [5] Christiansen, C.C. et al. (1999) Neues Jb. Miner. Abh., 175, 153-189. [6] Khomyakov, A.P. (1995) Mineralogy of hyperagpaitic alkaline rocks. Clarendon Press, UK

Novel crystal-chemical relations in layered Ti silicates.

CAMARA ARTIGAS, Fernando;
2010-01-01

Abstract

We consider structure topology for a group of Ti disilicates based on our single-crystal X-ray structure work on four Tidisilicate minerals, jinshajiangite, cámaraite, bornemanite and nechelyustovite, and two possible new mineral species with preliminary ideal formulae Na4BaTi2Nb(Si2O7)2O3(OH) (H2O)2 (mineral A) and Na3KBaTi2Nb(Si2O7)2O3(OH)(H2O)6 (mineral B). These minerals belong to a group of Ti silicates with a TS (titanium silicate) block [1-4]. Structure types of cámaraite, bornemanite, nechelyustovite and minerals A and B are new. The general formula of the TS block is AP 2BP 2MH 2MO 4(Si2O7)2X4+n, where MH 2 and MO 4 are cations of the H and O sheets; MH = Ti, Nb, Zr, Mn2+, Ca; MO = Ti, Zr, Fe2+, Mn2+, Ca, Na; AP and BP = cations at the peripheral (P) sites = Na, Ca, Ba, K; X = O, OH, F; n = 0,2,4 [4]. The TS block is composed of a central trioctahedral (O) sheet and two adjacent (H) sheets of [5-7]-coordinated polyhedra and (Si2O7) groups. All structures consist of a TS block and an I (intermediate) block that comprises atoms between two TS blocks. The I block consists of alkali and alkaline-earth cations, (H2O) groups and the oxyanions (PO4), (SO4) and (CO3). Structures of Ti disilicate minerals have been divided into four groups, each characterized by different linkage, content and stereochemistry of Ti (= Ti+Nb) in the TS block. In Groups I, II, III and IV, Ti = 1, 2, 3 and 4 apfu, respectively [4] In jinshajiangite and cámaraite, Ti = 2 apfu and the TS block exhibits the stereochemistry of Group II. In bornemanite, nechelyustovite, minerals A and B, Ti = 3 apfu, the TS block is as in Group III. Jinshajiangite contains one type of I block (as in perraultite); cámaraite, bornemanite and minerals A and B, two types of I block; nechelyustovite, three topologically and chemically different I blocks. The structures of nechelyustovite and mineral B contain a new (for TS-block minerals) type of I block, an array of H2O groups of ideal composition (H2O)5. Structures with a new type of TS block (more than one I block and more than one type of self-linkage of TS blocks) are related to structures of other minerals from the same Group: cámaraite, to bafertisite and jinshajiangite (Group II); bornemanite, to vuonnemite and barytolamprophyllite (Group III); nechelyustovite, to epistolite, barytolamprophyllite and a yet unknown structure (Group III); mineral A, to epistolite and barytolamprophyllite (Group III); mineral B, to barytolamprophyllite and a yet unknown structure. Minerals with a new type of TS-block structure and related minerals occur in the same environment and often form intimate intrgrowths. Discovery of five minerals with a new type of a TS-block structure (a) confirms that the chemical composition of the I block dictates the type of self-linkage of TS blocks [5]; (b) emphasizes the role of Ba Na exchange which results in changes in the topology of the I block and subsequently selflinkage of TS blocks (e.g. the bafertisite-cámaraitejinshgagiangite series); (c) enlarges the number of transformation-mineral series [6] due to Na-depletion, bornemanite ! nechelyustovite, Group III. [1] Belov, N.V. (1976) Essays on Structural Mineralogy. Nedra, Moscow. [2] Pyatenko, Yu. A. et al. (1976) Mineralogical crystal chemistry of titanium. Nauka, Moscow. [3] Egorov-Tismenko, Yu.K. & Sokolova, E.V. (1990) Mineral. Zh., 12(4), 40-49 (in Russian). [4] Sokolova, E. (2006). Can. Mineral., 44, 1273-1330. [5] Christiansen, C.C. et al. (1999) Neues Jb. Miner. Abh., 175, 153-189. [6] Khomyakov, A.P. (1995) Mineralogy of hyperagpaitic alkaline rocks. Clarendon Press, UK
2010
20th general meeting of the IMA
Budapest
21-27 August
Acta Mineralogica Petrographica ABSTRACT SERIES
University of Szeged
6
731
731
http://amp.mineralogy.hu/
Ti disilicate minerals; crystal structure
Cámara F; Sokolova E
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2318/84018
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact