Transmission electron microscopy has been used to characterize coexisting pyrophyllite and muscovite in low-grade metamorphosed pelites from Witwatersrand and northeastern Pennsylvania. The Witwatersrand sample consisted largely of porphyroblasts of interlayered muscovite and pyrophyllite in a fine-grained matrix of the same phases. In both textures, muscovite and pyrophyllite occurred as interlayered packets (with apparently coherent interfaces) from about 300 Å to a few micrometers in thickness, with no mixed layering. Their compositions were determined with a scanning transmission electron microscope to be

$$(\Box{_{{\rm{0}}{\rm{.11}}}}{\rm{ }}{{\rm{K}}_{{\rm{1}}{\rm{.72}}}}{\rm{Na}_{{\rm{0}}{\rm{.17}}})(A}{{\rm{l}}_{{\rm{3}}{\rm{.91}}}}{\rm{ F}}{{\rm{e}}_{{\rm{0}}{\rm{.03}}}}{\rm{M}}{{\rm{g}}_{{\rm{0}}{\rm{.05}}}}{\rm{T}}{{\rm{i}}_{{\rm{0}}{\rm{.01}}}}{\rm{)(S}}{{\rm{i}}_{{\rm{6}}{\rm{.11}}}}{\rm{ Al}}{{\rm{l}}_{{\rm{1}}{\rm{.89}}}}{\rm{)}}{{\rm{O}}_{{\rm{20}}}}{{\rm{(OH)}}_{\rm{4}}}$$

$$(\Box_{{\rm{1}}{\rm{.90}}}{\rm{N}}{{\rm{a}}_{{\rm{0.06}}}}{{\rm{K}}_{{\rm{0}}{\rm{.04}}}}{\rm{)(A}}{{\rm{l}}_{{\rm{3}}{\rm{.94}}}}{\rm{F}}{{\rm{e}}_{{\rm{0}}{\rm{.01}}}}{\rm{M}}{{\rm{g}}_{{\rm{0}}{\rm{.05}}}}{\rm{)(S}}{{\rm{i}}_{{\rm{7}}{\rm{.94}}}}{\rm{A}}{{\rm{l}}_{{\rm{0}}{\rm{.06}}}}{\rm{)}}{{\rm{O}}_{{\rm{20}}}}{{\rm{(OH)}}_{\rm{4}}},$$

The pyrophyllite and muscovite in the Pennsylvania shale likewise occurred only as coexisting coherent to sub-parallel packets as thin as 200 Å, with compositions of

$$(\Box_{{\rm{1}}{\rm{.89}}}{\rm{N}}{{\rm{a}}_{{\rm{0.04}}}}{\rm{C}}{{\rm{a}}_{{\rm{0}}{\rm{.02}}}}{{\rm{K}}_{{\rm{0}}{\rm{.05}}}}{\rm{)(A}}{{\rm{l}}_{{\rm{3}}{\rm{.93}}}}{\rm{F}}{{\rm{e}}_{{\rm{0}}{\rm{.04}}}}{\rm{M}}{{\rm{g}}_{{\rm{0}}{\rm{.02}}}}{\rm{T}}{{\rm{i}}_{{\rm{0}}{\rm{.01}}}}{\rm{)(S}}{{\rm{i}}_{{\rm{7}}{\rm{.92}}}}{\rm{A}}{{\rm{l}}_{{\rm{0}}{\rm{.08}}}}{\rm{)}}{{\rm{O}}_{{\rm{20}}}}{{\rm{(OH)}}_{\rm{4}}}$$

$$({\rm{N}}{{\rm{a}}_{{\rm{0}}{\rm{.04}}}}{\rm{C}}{{\rm{a}}_{{\rm{0}}{\rm{.02}}}}{{\rm{K}}_{{\rm{2}}{\rm{.03}}}}{\rm{)(A}}{{\rm{l}}_{{\rm{3}}{\rm{.54}}}}{\rm{F}}{{\rm{e}}_{{\rm{0}}{\rm{.24}}}}{\rm{M}}{{\rm{g}}_{{\rm{0}}{\rm{.16}}}}{\rm{T}}{{\rm{i}}_{{\rm{0}}{\rm{.06}}}}{\rm{)(S}}{{\rm{i}}_{{\rm{6}}{\rm{.09}}}}{\rm{A}}{{\rm{l}}_{{\rm{1}}{\rm{.91}}}}{\rm{)}}{{\rm{O}}_{{\rm{20}}}}{{\rm{(OH)}}_{\rm{4}}}.$$

The compositions of these coexisting pyrophyllite and muscovite define a solvus with steep limbs and extremely limited solid solution. Illite is a white mica, intermediate in composition between pyrophyllite and muscovite, formed at much lower temperatures than muscovite. These relations show that illite is metastable relative to pyrophyllite + muscovite in all of its diagenetic and low-grade metamorphic occurrences. This further implies that illite precursor phases, such as smectite, are also metastable. The prograde reactions involving smectite, illite, and muscovite are therefore inferred to represent Ostwald-step-rule-like advances through a series of metastable phases toward the equilibrium states attained in the greenschist facies. “Illite crystallinity” can therefore be a measure of reaction progress, for which temperature is only one of several determining factors.

The alteration of spodumene to cookeite has been identified in a Li-bearing aplite-pegmatite from northern Portugal. Optical microscopy and scanning and transmission electron microscopy (SEM/TEM) were used to characterize the alteration products in both cookeite + quartz and cookeite + kaolinite ± mica assemblages. Mutual relationships between the minerals were assessed using back-scattered electron imaging. The first assemblage occurs along the cleavage planes of spodumene, whereas the second forms as the result of spodumene breakdown. Fine mica grains surrounded the cookeite aggregates in the second assemblage only. Precipitations of cookeite and quartz in open pore spaces and parallel packets of cookeite and kaolinite were identified by TEM. Selected area electron diffraction carried out on cookeite identified a layer-stacking sequence from highly disordered to one-layer order-disorder with a lesser participation of two-layer polytypes. The thickness of one-layer cookeite packets averaged ∼85 −100 nm. Disordered cookeite has a mean thickness of 450 nm. The chemistry of cookeite was analyzed by both electron and ionmicroprobe techniques. The structural formula of cookeite from the first assemblage corresponds to: Al2.0(Si3.23Al0.766)O10(OH)2(Al1.80Li1.166Mg0.004Fe0.09)(OH)6. Two distinct compositional varieties were found: one corresponding to ideal cookeite, whereas the second belongs to the cookeite-donbassite join.

The thermodynamic stability field for the observed minerals was calculated using the SUPCRT® programme. Two distinct stages of cookeite crystallization are discussed. The lower pressure and temperature stability of the reaction of spodumene to cookeite + quartz were estimated at ∼2.4 kbar and 240°C. The cookeite + kaolinite ± mica assemblage is still in equilibrium with quartz at ∼2.2 kbar and 220°C. The lower limit for the stability of cookeite was found at 205°C and 2 kbar.

Feroxyhyte (δ′-FeOOH) is a relatively uncommon Fe oxide mineral and one of the few phases in the system Fe2O3-H2O for which thermodynamic properties are not known. In natural occurrences, it is always fine-grained, although samples with larger particle sizes and better crystallinity (labeled as δ-FeOOH) can be prepared in the laboratory. This contribution presents a thermochemical study on a series of feroxyhyte samples. One is fine-grained and poorly crystalline, similar to natural materials, while the other three are of better crystallinity. The enthalpy of formation of feroxyhyte at 298.15 K is −547.4±1.3kJ mol−1 for the poorly crystalline sample (surface area 88 m2/g), and −550.6±1.4, −550.9±1.3, and −552.6±1.2 kJ mol−1 for the samples with better crystallinity. The entropy of feroxyhyte can be estimated only crudely, because it is influenced to a great extent by its magnetic properties, particle size, and structural disorder. The $S_{298}^{\text{o}}$$S_{298}^{\rm{o}}$ of feroxyhyte is estimated here to be 65±5 J K−1 mol−1. The Gibbs free energy of the reaction feroxyhyte → hematite + liquid water is −7.4 to −12.6 kJ mol−1 at 298.15 K. The Gibbs free energy of formation ($\text{Δ}{G}_{\text{f}}^{\text{o}}$${\rm{\Delta }}G_{\rm{f}}^{\rm{o}}$) of the fine-grained, poorly crystalline feroxyhyte is −478.1±2.0 kJ mol−1 at 298.15 K. Since this sample is closest in its physical properties to natural feroxyhyte, this $\text{Δ}{G}_{\text{f}}^{\text{o}}$${\rm{\Delta }}G_{\rm{f}}^{\rm{o}}$ value should be used in thermodynamic modeling related to processes involving naturally occurring feroxyhyte. In terms of Gibbs free energy and enthalpy, feroxyhyte is very similar to lepidocrocite and maghemite, and, like these two phases, has no thermodynamic stability field in the system Fe2O3-H2O, except possibly at the nanoscale.

Soil profiles developed in different climates and physical settings are highly variable in structure, in mineralogy, in the local biosphere and in the compositions of the soil gas and water phases. Discussion of metals in ‘the weathering environment’ needs to acknowledge and address this diversity.

The thermochemical methods developed by Pourbaix (1949) and Garrels and Christ (1965) remain useful predictors of metal speciation and solubility but the approach is valid only for processes involving carbonates, sulphides, hydroxides and similar minerals in soils and sediments. Almost no primary silicates are thermodynamically stable: they spontaneously decompose to non-equilibrium solid products with metal release determined by kinetics.

Hydrolysis constants for aquo-complexes are useful indicators of metal speciation, mobility and availability. Recent work on soluble soil organic matter confirms that the active ligands are overwhelmingly oxygen based: phenols, carboxylic acids, alcohols. Many of these molecules compete very effectively with aquo-complexes to form strong metal chelates and appear to be responsible for substantial Al and Fe mobilization within and translocation down soil profiles.

It is important to note also that strong clay mineral/organic matter associations (clay-organic complex) will fix metals as a consequence of the same chelation reactions (in this case removing them from solution - retardation).

The potential for engineering stable proteins with multiple amino acid substitutions was explored. Eleven lysine, five methionine, two tryptophan, one glycine, and three threonine substitutions were simultaneously made in barley chymotrypsin inhibitor-2 (CI-2) to substantially improve the essential amino acid content of the protein. These substitutions were chosen based on the three-dimensional structure of CI-2 and an alignment of homologous sequences. The initial engineered protein folded into a wild-type-like structure, but had a free energy of unfolding of only 2.2 kcal/mol, considerably less than the wild-type value of 7.5 kcal/mol. Restoration of the lysine mutation at position 67 to the wild-type arginine increased the free energy of unfolding to 3.1 kcal/mol. Subsequent cysteine substitutions at positions 22 and 82 resulted in disulfide bond formation and a protein with nearly wild-type thermodynamic stability (7.0 kcal/mol). None of the engineered proteins retained inhibitory activity against chymotrypsin or elastase, and all had substantially reduced inhibitory activity against subtilisin. The proteolytic stabilities of the proteins correlated with their thermodynamic stabilities. Reduction of the disulfide bond resulted in substantial loss of both thermodynamic and proteolytic stabilities, confirming that the disulfide bond, and not merely the cysteine substitutions, was responsible for the increased stability. We conclude that it is possible to replace over a third of the residues in CI-2 with minimal disruption of stability and structural integrity.