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.

Structure and Mineralogy of Clay Minerals

Characterization of the manganese oxide produced by Pseudomonas putida strain MnB1

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.

Chapter 2 Structures and Mineralogy of Clay Minerals

Relations Between Iron Oxides, Soil Color, and Soil Formation

Todorokite-type MnO2 as a zinc-ion intercalating material

Vernadite (MnO2·nH2O) is a mineral with a poorly ordered structure. Its synthetic analogue is designated δ-MnO2. Birnessite and vernadite are independent mineral species and cannot be described further under the same name. They have similar hexagonal unit-cell parameters, a0, but different c0 parameters. Rancieite has a structure similar to that of birnessite. Calcium bearing, 14-A birnessite occurring in nature was first described by the authors. In addition to the todorokite having the parameters a0 = 9.75 A, b0 = 2.84 A, and c0 = 9.59 A, other species of natural todorokite are known having a0 parameters that are multiples of 4.88 A equal to 14.6 and 24.40 A, the b0 and c0 parameters being the same.

Manganese minerals in clays; a review

Two modifications of the delta-hydroxide of iron have been synthesized under laboratory conditions. Both are formed topotactically by the rapid course of the abiogenic reaction of the oxidation of Fe+2 at the expense of Fe(OH)2. Natural δ'-FeOOH, for which the authors propose the name "feroxyhyte," was found as yellowish-brown deposits in iron-manganese nodules from the bottom of the Pacific Ocean, Baltic, White, and Kara seas, and in gley soils. Feroxyhyte is an unstable hydrous oxide of iron, apparently transformed spontaneously into goethite, the stable modification of FeOOH. Its theoretical composition is Fe2O3 - 89.86, H2O - 10. 147%.

Feroxyhyte, a new modification of FeOOH

was analyzed by M6ssbauer spectroscopy, magnetization and magnetic susceptibility measurements. The iron is entirely ferric, and the main feature of the M6ssbauer spectrum at room temperature is a single absorption line with isomer shift 6 = 0.36(1) mm/sec due to iron in M2 sites. The line is broadened by a slight quadrupole splitting A = 0.18(1) mm/sec, the smallest yet reported for a sheet silicate. Weaker features corresponding to quadrupole doublets with relative intensities of 7% and 8% having 6 = 0.43(1) mm/sec; A = 1.22(2) mm/sec and 6 = 0.14(1) m m/sec; A = 0.59(2) mm/sec are assigned to ferric iron in nonequivalent octa- hedral and tetrahedral sites, respectively, giving the following formula, based on published chemical analysis: Cao.o5(Fe 3+

Cation Distribution, Mössbauer Spectra, and Magnetic Properties of Ferripyrophyllite

The formation of authigenic manganese minerals and ores in the pelagic regions of the ocean is related to oxidation of Mn2+ extracted from basalts and other rocks with heated seawater. For littoral parts of the ocean and lakes mobilization of Mn2+ and Fe2+ is admitted finding its way to the bottom sediments (along with the organic substances) from land in the form of Mn4+. The main manganese mineral of oceanic and continental basins is vernadite. Its deposition is considered a result of the activity of microorganisms.

Contributions to the mineralogy of authigenic manganese phases from marine manganese deposits

In iron-manganese nodules from the floor of Pacific ocean, Baltic, White Sea and Kara Sea, iron bydroxide δ'-FeOOH was analysed in the laboratory. In buried ooze, reduction processes generate Fe(HCO3)2 which migrates into the upper part of the bottom ooze and into near bottom sea water where Fe(OH)2 is formed. The oxidation process of Fe2+ to Fe3+, without participation of iron bacteria, leads to the topotactic transformation of Fe(OH)2 to δ'-FeOOH. Marine water does not contain Fe2+ and cannot be a direct source of iron deposited in the nodules. Discovery of δ'-FeOOH in marine nodules permits the consideration that both iron and manganese were derived from the buried bottom mud, which during diagenetic processes led to the transfer of these metals in solutions and their upward migration.

F. V. Chukhrov

Papers

Manganese minerals in clays; a review

Feroxyhyte, a new modification of FeOOH

Cation Distribution, Mössbauer Spectra, and Magnetic Properties of Ferripyrophyllite

Contributions to the mineralogy of authigenic manganese phases from marine manganese deposits

Mineralogical criteria in the origin of marine iron-manganese nodules