The thermodynamic properties of 254 end-members, including 210 mineral end-members, 18 silicate liquid end-members and 26 aqueous fluid species are presented in a revised and updated internally consistent thermodynamic data set. The PVT properties of the data set phases are now based on a modified Tait equation of state (EOS) for the solids and the Pitzer & Sterner (1995) equation for gaseous components. Thermal expansion and compressibility are linked within the modified Tait EOS (TEOS) by a thermal pressure formulation using an Einstein temperature to model the temperature dependence of both the thermal expansion and bulk modulus in a consistent way. The new EOS has led to improved fitting of the phase equilibrium experiments. Many new end-members have been added, including several deep mantle phases and, for the first time, sulphur-bearing minerals. Silicate liquid end-members are in good agreement with both phase equilibrium experiments and measured heat of melting. The new dataset considerably enhances the capabilities for thermodynamic calculation on rocks, melts and aqueous fluids under crustal to deep mantle conditions. Implementations are already available in thermocalc to take advantage of the new data set and its methodologies, as illustrated by example calculations on sapphirine-bearing equilibria, sulphur-bearing equilibria and calculations to 300 kbar and 2000 °C to extend to lower mantle conditions.

An improved and extended internally consistent thermodynamic dataset for phases of petrological interest, involving a new equation of state for solids

X-ray Diffraction Procedures for Clay Mineral Identification

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

The two rock-forming polymorphs of serpentine Mg3Si2O5(OH)4, lizardite and chrysotile, occur in nature in virtually identical ranges of temperature and pressure, from surficial or near-surficial environments to temperatures perhaps as high as 400°C. Laboratory evidence indicates that lizardite is the more stable at low temperatures, but the difference in their Gibbs free energies is not more than about 2 kJ in the 300-400°C range. Above about 300°C, antigorite + brucite is more stable than both; in other words, chrysotile is nowhere the most stable. The crystal structures of lizardite and chrysotile give rise to contrasting crystallization behaviors and hence modes of occurrence. The hydration of peridotite at low temperature results in the growth of lizardite from olivine, and (commonly topotactically) from chain and sheet silicates, although the MgO-SiO2-H2O (MSH) phase diagram predicts antigorite + talc in bastite. The activity of H2O during serpentinization may be buffered to low values by the solids,...

The serpentinite multisystem revisited : chrysotile is metastable

Serpentinization of abyssal peridotites at mid-ocean ridges

Chemical, X-ray, electron optical, and infrared analyses have been made on twenty antigorites form the Nishisonogi and Sasaguri areas, northern Kyushu, Japan, along with two antigorites from other localities. The indexed X-ray powder patterns give various supercell A parameters (A = 35.4–47.2A) as well as varying subcell dimensions (a = 5.42–5.46, b = 9.24–9.26, c = 7.24–7.28A, (β = 91.3–91.7°). When the ratio of A⁄a is represented by M (M = 6.5–8.7), the electron diffraction patterns can be classified into M = n (n is integer), M = (2n + 1)/2, and M ≠n⁄2 types. The minerals with these different types of M aggregate to form common antigorite specimens. The well-known A = 43A antigorite belongs to the M = n type. Single crystal X-ray and electron diffraction patterns indicate that the true superstructure periodicity along the X axis of the antigorites giving M = (2n + 1)/2 type patterns, which may contain odd-numbered octahedra in the one alternating-wave, is 2A (corresponding to two waves) and the space lattice is C-centered. This lattice seems to give more reasonable structures at the inversion points of the alternating-waves than hitherto predicted (Kunze, 1961). The M ≠n⁄2 type patterns may be caused by coherent domains with different A parameters of the former two types. The structural formula of antigorite can be given by Mg6Si4(1 + 1/2M)O10(1+1/2M)(OH)8-2M. Octahedral Mg is substituted by Fe2+, and Al or trivalent cations substitute for both the tetrahedral and octahedral cations, although the trivalent cations may be contained more in the octahedral positions for most materials. Larger Fe2+ content (FeO 5.5% in max.) tends to bring larger a and b, but smaller c and M(A) parameters. The small c is also produced by relatively large Al contents (Al2O3 4.1% in max.), which supports the presence of tetrahedral Al together with the infrared 3570 cm−1 band. The main OH band at 3685–3674 cm−1 tends to decrease in frequency with increasing Fe content and decreasing M parameter. The correlations of the Fe contents to the a and M parameters and to the main OH band are somewhat different between the Nishisonogi and Sasaguri antigorites, which are discussed in relation to their formation conditions.

Variations in chemical composition and structural properties of antigorites.

X-ray powder patterns and cell dimensions of some chlorites in japan, with a note on their interference colors

One dimensional refinement and infrared OH band investigation have been made on five orthochlorites of the Mg–Fe series and on two Mg-leptochlorites with substitution of 2Al for 3Mg. The results indicate that the leptochlorites have cation vacancies in the interlayer sheet. Octahedral Al is concentrated in the interlayer sheet in every sample, but considerable amounts of Al are contained also in the 2: 1 octahedral sheet in the Al- and/or Fe-rich chlorites, which suggests a relatively narrow layer charge range in chlorites. The variation of cation composition of the tetrahedral and octahedral sheets results in variation of the sheet thickness and the interlayer O–OH space: with increasing tetrahedral Al (generally octahedral Al also increases), the two octahedral sheet thicknesses and the O–OH space decrease, but the tetrahedral sheet thickness increases; larger Fe2+ content brings about thicker octahedral and thinner tetrahedral sheets and smaller O–OH space.The O–OH space, which primarily determines the d(001) spacing, is concluded to be controlled by both the surplus negative charge of 2 : 1 layer surface oxygens and the interlayer octahedral cations; the former is caused by the tetrahedral Al substitution for Si and is affected also by the 2 : 1 octahedral cations. The OH bands and tetrahedral ordering of amesite and the O–OH spaces of dioctahedral chlorites and of some 1 : 1 layer silicates are discussed along with those of trioctahedral chlorites.

Cation distribution, sheet thickness, and O-OH space in trioctahedral chlorites - an X-ray and infrared study.

Vibrations involving hydroxyls in the infrared spectra of two synthetic 7 A trioctahedral minerals (amesite and aluminian lizardite) and of seven natural 14 A minerals (five trioctahedral chlorites of the Mg–Fe series, sudoite, and cookeite) have been investigated by comparison of the spectra with those of partially deuterated forms obtained by hydrothermal treatments with D2O. The results are interpreted to indicate that the OH bands between 850 cm−1 and 600 cm−1 in the trioctahedral minerals arise from librations of the outer OH in the 7 A minerals or the interlayer OH in the 14 A minerals, expressed by (SiAl)O–OH (∼800 cm−1) and (SiSi)O–OH (∼720 cm−1), and of the inner OH in the 7 A minerals or the 2 : 1 layer OH in the 14 A minerals (∼650 cm−1). These librations are correlated with the OH stretching vibrations in a reversed frequency relation. The shoulders around 930 cm−1 in sudoite and cookeite are confirmed to be due to the dioctahedral 2 : 1 OH. Some additional information on the OH stretching bands and on the lattice vibration bands has also been obtained.

Haruo Shirozu

Papers

Variations in chemical composition and structural properties of antigorites.

X-ray powder patterns and cell dimensions of some chlorites in japan, with a note on their interference colors

Cation distribution, sheet thickness, and O-OH space in trioctahedral chlorites - an X-ray and infrared study.

Infrared study of some 7.ANGS. and 14.ANGS. layer silicates by deuteration.

Mg-CHLORITE AND INTERSTRATIFIED Mg-CHLORITE/SAPONITE ASSOCIATED WITH KUROKO DEPOSITS