Boris Borisovich Zvyagin

Bio: Boris Borisovich Zvyagin is an academic researcher. The author has contributed to research in topics: Mineral hydration & Clay minerals. The author has an hindex of 1, co-authored 1 publications receiving 136 citations.

Structure and Mineralogy of Clay Minerals

Abstract: Phyllosilicates, and among them clay minerals, are of great interest not only for the scientific community but also for their potential applications in many novel and advanced areas. However, the correct application of these minerals requires a thorough knowledge of their crystal chemical properties. This chapter provides crystal chemical and structural details related to phyllosilicates and describes the fundamental features leading to their different behaviour in different natural or technical processes, as also detailed in other chapters of this book. Phyllosilicates, described in this chapter, are minerals of the (i) kaolin-serpentine group (e.g. kaolinite, dickite, nacrite, halloysite, hisingerite, lizardite, antigorite, chrysotile, amesite, carlosturanite, greenalite); (ii) talc and pyrophyllite group (e.g. pyrophyllite, ferripyrophyllite); (iii) mica group, with particular focus to illite; (iv) smectite group (e.g. montmorillonite, beidellite, nontronite, saponite, hectorite, sauconite); (v) vermiculite group; (vi) chlorite group; (vii) some 2:1 layer silicates involving a discontinuous octahedral sheet and a modulated tetrahedral sheet such as kalifersite, palygorskite and sepiolite; (viii) allophane and imogolite and (ix) mixed layer structures with particular focus on illite-smectite.

The distribution of octahedral cations in the 2:1 layers of dioctahedral smectites studied by oblique-texture electron diffraction

Abstract: Olique-texture electron diffraction examination of K-saturated dioctahedral smectites after 70-100 wetting-drying cycles allows the determination of cation distribution between trans and cis octahedra of the 2:1 layers. Studies of smectites with different compositions has revealed a wide variety of occupancies of the available octahedral sites. In dioctahedral phyllosilicates only two of the three symmetrically independent octahedral positions are occupied by cations. The 2:1 layer will have a centre of symmetry if the trans octahedra are vacant (model 1, Fig. la) and it will have none if the cations occupy trans octahedral sites as well as cis octahedral positions, forming one of the two regular systems of points (model 2, Fig. lb). Numerous structure refinements of dioctahedral layer-silicates have shown that the octahedral cations occupy only the cis octahedrat positions of the 2:1 layers if the total number of these cations per unit cell is equal to 4. The probable existence of two-layer micas with non-centrosymmetrical layers was noted by B. B. Zvyagin et al. (1979); these authors also specified the possible polytypes of micas with such layers and calculated their diffraction data for ideal models.

Chapter 2 Structures and Mineralogy of Clay Minerals

Abstract: Publisher Summary This chapter describes structures and mineralogy of clay minerals. Phyllosilicates considered in this chapter ideally contain a continuous tetrahedral sheet. Each tetrahedron consists of a cation, T, coordinated to four oxygen atoms and linked to adjacent tetrahedra by sharing three corners (the basal oxygen atoms, Ob) to form an infinite two-dimensional hexagonal mesh pattern along the a, b crystallographic directions. The free corners (the tetrahedral apical oxygen atoms, Oa) of all tetrahedra point to the same side of the sheet and connect the tetrahedral and octahedral sheets to form a common plane with octahedral anionic position Ooct. Ooct anions lie near to the center of each tetrahedral 6-fold ring, but are not shared with tetrahedra. The 1:1 layer structure consists of the repetition of one tetrahedral and one octahedral sheet, while in the 2:1 layer structure one octahedral sheet is sandwiched between two tetrahedral sheets. In the 1:1 layer structure, the unit cell includes six octahedral sites (i.e., four cis and two trans-oriented octahedral) and four tetrahedral sites. Six octahedral sites and eight tetrahedral sites characterize the 2:1 layer unit cell. Structures with all the six octahedral sites occupied are known as “trioctahedral.” If only four of the six octahedra are occupied, the structure is referred to as “dioctahedral.” The structural formula is often reported based on the half unit-cell content—that is, it is based on three octahedral sites.