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COMPOSITIONAL AND STRUCTURAL VARIATION OF SUDOITE FROM THE BETIC CORDILLERA (SPAIN): A TEM/AEM STUDY

¹ Departamento de Química Inorgánica, Cristalografía y Mineralogía, Facultad de Ciencias, Campus de Teatinos, Universidad de Málaga, Spain
² Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, Facultad de Ciencias, 18071 Granada, Spain

^* E-mail address of corresponding author: mdruiz{at}uma.es

Sudoite from diagenetic to very low-grade metaclastites of the Betic Cordillera was studied by X-ray diffraction and transmission/analytical electron microscopy. Sudoite formed directly from dickite, the assemblage dickite + sudoite + illite being replaced at increasing metamorphic grade by the assemblage pyrophyllite + sudoite + illite. Sudoite ranges in composition from Mg-rich to Fe-rich chemistries. In addition, a wide variety of mixed-layered structures (illite-sudoite, pyrophyllite-sudoite, and dickite-sudoite) was also identified. Mg-rich sudoite shows a mean chemical composition of (Al_2.91Fe²⁺ _0.25Mg_1.80)(Si_3.10Al_0.90)O₁₀(OH)₈, and a IIb ordered structure with b = 9.055 Å. Intermediate Fe-Mg sudoite exhibits a very variable composition, the Fe-rich phases having a mean composition of (Al_2.09Fe³⁺ _0.61Fe²⁺ _0.87Mg_1.44)(Si_3.31Al_0.69O₁₀(OH)₈. These are disordered polytypes with b values ranging from 9.070 to 9.101 Å. Fe occurs in both octahedral sheets, according to two types of substitutions: Fe³⁺ for Al in the dioctahedral sheet and Fe²⁺ for Mg in the trioctahedral sheet. Sudoite with such a composition has not been described previously.

Key Words: Betic Cordillera • Dickite • Illite • Mixed-layer • Pyrophyllite • Spain • Sudoite

This article has been cited by other articles:

				M. D. Ruiz Cruz, M. D. Rodriguez, and J. K. Novak The illitization of dickite: chemical and structural evolution of illite from diagenetic to metamorphic conditions European Journal of Mineralogy, April 1, 2009; 21(2): 361 - 372. [Abstract] [Full Text] [PDF]

				J. Kameda, R. Miyawaki, R. Kitagawa, and T. Kogure XRD and HRTEM analyses of stacking structures in sudoite, di-trioctahedral chlorite American Mineralogist, October 1, 2007; 92(10): 1586 - 1592. [Abstract] [Full Text] [PDF]