Structures of Layer Silicates

A new method for collecting complete three-dimensional electron diffraction data is described. Diffraction data is collected by combining electron beam tilt at many very small steps, with rotation of the crystal in a few but large steps. A number of practical considerations are discussed, as well as advantages and disadvantages compared to other methods of collecting electron diffraction data.

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Collecting 3D electron diffraction data by the rotation method

Infrared Spectroscopy of Minerals and Related Compounds

Changes in the mechanisms of formation and global distribution of phyllosilicate clay minerals through 4.567 Ga of planetary evolution in our solar system reflect evolving tectonic, geochemical, and biological processes. Clay minerals were absent prior to planetesimal formation ~4.6 billion years ago but today are abundant in all near-surface Earth environments. New clay mineral species and modes of clay mineral paragenesis occurred as a consequence of major events in Earth’s evolution—notably the formation of a mafic crust and oceans, the emergence of granite-rooted continents, the initiation of plate tectonics and subduction, the Great Oxidation Event, and the rise of the terrestrial biosphere. The changing character of clay minerals through time is thus an important part of Earth’s mineralogical history and exemplifies the principles of mineral evolution.

Clay mineral evolution

The field of atomic-resolution transmission electron microscopy and its application to materials science is reviewed. This technique, whose spatial resolution is now about one Angstrom, is valuable wherever nanoscale characterization of materials is needed. The history of the subject is briefly outlined, followed by a discussion of experimental techniques. Resolution-limiting factors are summarized, together with the underlying theory of image formation. Seven promising approaches to super-resolution are reviewed. The statistical principles of quantitative image analysis and defect modelling are outlined for both HREM and STEM. Methods for obtaining defect energies from images are discussed. The review ends with a summary of some recent applications, including such topics as the Fullerenes, nanotubes, dislocation kink imaging, superconductors, atomic-resolution imaging of whole semiconductor devices, the study of atomic defects in mediating first-order phase transitions, collosal magnetoresistance, ceramic interfaces, quasicrystals, imaging of surfaces, glasses, catalysts and magnetic materials.

The future of atomic resolution electron microscopy for materials science

Borocookeite, ideally Li 1+3 x Al 4– x (BSi 3 )O 10 (OH,F) 8 (where “ x ” varies in the range 0.00–0.33 apfu), in which [4] Al is replaced by B relative to cookeite, occurs as a late-stage pocket mineral in the Sosedka and Mokhovaya pegmatite veins, Malkhan gem tourmaline deposit, Chikoy district, Chita oblast, Russia. Borocookeite proper, as well as boron-rich cookeite, is light grey with a pinkish or yellow hue and occurs as a dense, massive crypto-flaky aggregate or thin crusts and snow-like coatings on crystals of quartz, tourmaline, and feldspars from miarolitic cavities. Fragments of elbaite, danburite, and albite are included in the borocookeite mass. In some pockets, the coating is composed of borocookeite and boron-rich muscovite (or boromuscovite) which are not distinguishable visually. Chemical analysis yields (wt%): SiO 2 34.19, TiO 2 0.02, Al 2 O 3 41.77, FeO 0.06, MnO 0.07, MgO 0.04, CaO 0.08, Na 2 O 0.01, K 2 O 2 O 4.65, Rb 2 O 0.004, Cs 2 O 0.005, B 2 O 3 4.06, BeO 0.05, H 2 O + 14.17, H 2 O– 0.11, F 1.22, −O = F 0.51, total 100.00. The empirical formula calculated on the basis of 28 positive charges is: Li 1.61 Al 3.80 (Al 0.44 B 0.60 Be 0.01 Si 2.95 ) ∑ 4.00 O 10 [F 0.33 (OH) 7.81 ] ∑ 8.14 . The unit- cell parameters, calculated from X-ray powder diffraction data, are a = 5.110(4), b = 8.856(3), c = 14.080(6) A, β = 96.93° (4) these values are smaller than those for cookeite. D calc = 2.69(1) g/cm 3 . The mineral has a Mohs hardness of 3, light pinkish-grey streak, greasy luster, perfect (001) cleavage, and no parting or fracture. Optical properties (for white light): α = 1.574, β = 1.580, γ = 1.591 (all ± 0.002), 2 V calc = 72°, dispersion not determined. The optical sign and the angle of the optical axis were not measured because of the small size and strong curvature of the mineral flakes. Borocookeite, as well as other boron-rich phyllosilicate minerals, crystallized from evolved residual solutions in miarolitic cavities at temperatures not less 265–240 ° C. The ratio of activities of K, Li, B, F, and H 2 O in the mineral-forming fluids of isolated evolving pockets determined whether borocookeite or boromuscovite formed separately or together.

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Borocookeite, a new member of the chlorite group from the Malkhan gem tourmaline deposit, Central Transbaikalia, Russia

A di,trioctahedral Li-chtorite cookeite (Lio.?Alr.r )r.s(Alr.r"Fe;.tnFe3.+or), ,rISi, ,rAlo u2],.oO,o . (OH)t"u, with an exceptionally perfect crystal structure has been found in bauxite of Djalair (Middle Asia). High-voltage diffraction (oblique-texture) patterns were used for its structural identification. It was established that it is a oneJayer triclinic polytype lo'uo'rlraraloLoll ..w i t h s y m m e t r y C i a n d u n i t c e l l : a 5 . 1 4 , b : 8 . 9 0 , c : l 4 . l 5 A , a : 9 0 o 3 3 ' , A : 9 6 " 1 2 ' , 1 = 90'. The small deviation ofa from 90o results in very peculiar features ofthe diffraction patterns, giving the false impression of a monoclinic lattice but with two non-selfconsistent Bvalues. The formation of the cookeite investigated is the final result of a peculiar transformation of bauxite rock following an intermediate stage of formation of a two-layer monoclinic pyrophyllite polytype.

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Cookeite with a perfect regular structure, formed by bauxite alteration

Modules (P) and (S) which taken separetely constitute the structures of pyroxene and spinel respectively, may give rise, in combination, to a wide polysomatic system ranging between these two minerals as end members The system is firstly discussed on the basis of complex layers (P m S n P m ), built up by somatic parts of both spinel and pyroxene, from the ((P/2)S(P/2)) modules, which are the OD layers giving rise to the sapphirine family, to the general (P m / 2 S n P m/2 ), which includes ((P/2)S n (P/2)) (characterizing the structure of calcium aluminium ferrite and SFCA-I compound) and (PSP) (characterizing the surinamite-type structures) Afterwards the system is discussed on the basis of (P m ) and (S n ) layers, with derivation of a new polytypic family closely related to that of sapphirine Finally the possible stacking sequences of single modules (S), giving rise to the spinelloid series and the stacking and condensation of single (P) modules, giving rise to the whole biopyriboles series, are presented and discussed

The pyroxene-spinel polysomatic system

The use of Imaging Plates (IP) signifies great progress for electron diffraction structure analysis (EDSA). This is evidenced and verified in case of brucite Mg(OH) 2 studied earlier by means of electron diffractometry. Actual problems and real perspectives in the development of EDSA based on IP are outlined.

Imaging plates – a new life for electron diffraction structure analysis

The role of electron diffraction structure analysis in mineralogy is discussed with special reference to developments in the former Soviet Union and the current Russian Federation.

Boris B. Zvyagin

Papers

Borocookeite, a new member of the chlorite group from the Malkhan gem tourmaline deposit, Central Transbaikalia, Russia

Cookeite with a perfect regular structure, formed by bauxite alteration

The pyroxene-spinel polysomatic system

Imaging plates – a new life for electron diffraction structure analysis

Minerals - a special area of electron diffraction structure analysis