Abstract
Nacrite crystals from a vug within a matrix of dickite at Red Mountain near Sil verton, Colorado, have a = 8.906(2), b = 5.146(1), c = 15.664(3) Å, β = 113.58(3)°, V = 657.9(3) Å3, and space group Cc. The structure was solved by direct methods to determine phase angles, followed by electron density maps to locate all atoms. Refinement by least-squares ceased at R = 4.5%. Each 7 Å layer has structural detail very similar to those of dickite and kaolinite, although nacrite stacking is based on — a/3 interlayer shifts along the 8.9 Å axis (with octahedral cations alternating between the I and II sites in successive layers), whereas dickite and kaolinite are based on shifts of — a/3 along the 5.1 Å axis (with octahedral cations in the same set of sites in each layer). The angle of tetrahedral rotation is 7.8°, and the octahedral counterrotations are 7.6° and 8.1°. The H+ protons were located on DED maps. The inner 0..H1 vector points exactly toward the vacant octahedron and is depressed — 18.6° away from the level of the octahedral cations. All three surface OH groups have 0...H vectors at 50° to 66° to (001), although OH2 may not participate in interlayer hydrogen bonding. All three interlayer OH-H-O contacts are bent to angles between 132° and 141° and form contacts between 2.94 and 3.12 Å. The interlayer separation of 2.915 Å is slightly larger than in dickite, interpreted as due to a less favorable meshing of the oxygen and hydroxyl surfaces in nacrite—a direct consequence of layer shifts along the 8.9 Å axis.
Similar content being viewed by others
References
Bailey, S. W. (1963) Polymorphism of the kaolin minerals: Amer. Mineral. 48, 1196–1209.
Bailey, S. W. (1969) Polytypism of trioctahedral 1:1 layer silicates: Clays & Clay Minerals 17, 355–371.
Bailey, S. W. and Tyler, S. A. (1960) Clay minerals associated with the Lake Superior iron ores: Econ. Geol. 55, 150–175.
Blount, A. M., Threadgold, I. M., and Bailey, S. W. (1969) Refinement of the crystal structure of nacrite: Clays & Clay Minerals 17, 185–194.
Bühmann, D. (1988) An occurrence of authigenic nacrite: Clays & Clay Minerals 36, 137–140.
Giese Jr, R. F. (1973) Interlayer bonding in kaolinite, dickite and nacrite: Clays & Clay Minerals 21, 145–149.
Giese Jr., R. F. (1988) Kaolin minerals: Structures and stabilities: Chapter 3 in Hydrous Phyllosilicates (Exclusive of Micas), S. W. Bailey, ed., Reviews in Mineralogy 19, Mineralogical Society of America, Washington, D.C., 29–66.
Giese Jr, R. F. and Datta, P. (1973) Hydroxyl orientation in kaolinite, dickite, and nacrite: Amer. Mineral. 58, 471–479.
Gruner, J. (1933) The crystal structure of nacrite and a comparison of certain optical properties of the kaolin group with its structures: Zeit. Kristallogr. 85, 345–354.
Hendricks, S. B. (1939) The crystal structure of nacrite Al2O3 2SiO2 • 2H2O and the polymorphism of the kaolin minerals: Zeit. Kristallogr. 100, 509–518.
Ladd, M. F. C. and Palmer, R. A. (1977) Structure Determination by X-ray Crystallography: Plenum, New York, 393 pp.
Marumo, K. (1989) Genesis of kaolin minerals and pyrophyllite in Kuroko deposits of Japan: Implications for the origins of the hydrothermal fluids from mineralogical and stable isotope data: Geochim. Cosmochim. Acta 53, 2915–2924.
Newnham, R. E. (1961) A refinement of the dickite structure and some remarks on polymorphism in kaolin minerals: Mineral. Mag. 32, 683–704.
Permyakov, V. M. (1936) Über hydrothermale Synthese des Kaolins (in Russian): Acad. Sci. USSR, Vernadsky Jubilee Vol., 563–580.
Radoslovich, E. W. (1963) The cell dimensions and symmetry of layer-lattice silicates. IV. Interatomic forces: Amer. Mineral. 48, 76–99.
Ushatinskiy, I. N., Babitsyn, P. K., and Kiesleva, F. P. (1973) Dickite and nacrite in Mesozoic deposits of western Siberia: Akad. Nauk SSSR, Doklady Earth Sci. Section 209, 107–109.
Zheng, H. and Bailey, S. W. (1989) Structures of intergrown triclinic and monoclinic IIb chlorites from Kenya: Clays & Clay Minerals 37, 308–316.
Zvyagin, B. B., Soboleva, S. V., and Fedotov, A. F. (1972) Refinement of the structure of nacrite by high-voltage electron diffraction: Soviet Phys. Cryslall. 17, 448–452.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Zheng, H., Bailey, S.W. Refinement of the Nacrite Structure. Clays Clay Miner. 42, 46–52 (1994). https://doi.org/10.1346/CCMN.1994.0420106
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1346/CCMN.1994.0420106