Stephen Guggenheim

BASELINE STUDIES OF THE CLAY MINERALS SOCIETY SOURCE CLAYS: THERMAL ANALYSIS

Thermal analysis involves a dynamic phenomenological approach to the study of materials by observing the response of these materials to a change in temperature. This approach differs fundamentally from static methods of analysis, such as structural or chemical analyses, which rely on direct observations of a basic property of material ( e.g. crystal structure or chemical composition) at a well-defined set of conditions ( e.g. temperature, pressure, humidity). Clay minerals are highly susceptible to significant compositional changes in response to subtle changes in conditions. For example, changes in the fugacity of water affect the stability of interlayer H2O in a clay mineral (see below). Therefore, care must be taken that all experimental conditions are known with accuracy and precision. Differential thermal analysis (DTA), thermal gravimetric analysis (TG or TGA), and derivative thermal gravimetric (DTG) analysis are reported for each of the eight Source Clay minerals using commonly available commercial instruments. The DTA curves show the effect of energy changes (endothermic or exothermic reactions) in a sample. For clays, endothermic reactions involve desorption of surface H2O ( e.g. H2O on exterior surfaces) and dehydration ( e.g. interlayer H2O) at low temperatures (<100°C), dehydration and dehydroxylation at more elevated temperatures, and, eventually, melting. Exothermic reactions are related to recrystallization at high temperatures that may be nearly concurrent with or after dehydroxylation and melting. Discriminating between desorption and dehydration or dehydration and dehydroxylation may be problematic. The TG curves ideally show only weight changes during heating. The derivative of the TG curve, the DTG curve, shows changes in the TG slope that may not be obvious from the TG curve. Thus, the DTG curve and the DTA curve may show strong similarities for those reactions that involve weight and enthalpy changes, such as desorption, dehydration and dehydroxylation reactions. In …

SUMMARY OF RECOMMENDATIONS OF NOMENCLATURE COMMITTEES RELEVANT TO CLAY MINERALOGY: REPORT OF THE ASSOCIATION INTERNATIONALE POUR L'ETUDE DES ARGILES (AIPEA) NOMENCLATURE COMMITTEE FOR 2006

Brindley et al. (1951) reported the earliest efforts to obtain international collaboration on nomenclature and classification of clay minerals, initiated at the International Soil Congress in Amsterdam in 1950. Since then, national clay groups were formed, and they proposed various changes in nomenclature at group meetings of the International Clay Conferences. Most of the national clay groups have representation on the Nomenclature Committee of the Association Internationale pour l’Etude des Argiles (AIPEA, International Association for the Study of Clays), which was established in 1966. The precursor committee to the AIPEA Nomenclature Committee was the Nomenclature Subcommittee of the Comite International pour l’Etude des Argiles (CIPEA, International Committee for the Study of Clays). The AIPEA Nomenclature Committee has worked closely with other international groups, including the Commission on New Minerals and Mineral Names (CNMMN) of the International Mineralogical Association (IMA), which is responsible for the formal recognition of new minerals and mineral names, and the International Union of Crystallography (IUCr), which considered extensions to the nomenclature of disordered, modulated and polytype structures (Guinier et al. , 1984) published earlier by a joint committee with the IMA (Bailey, 1977). In contrast to the other national clay groups, however, The Clay Minerals Society (CMS) Nomenclature Committee, which was established in 1963 at the same time as the CMS and predates the AIPEA Nomenclature Committee, remains in existence and occasionally produces recommendations. The precursor to this committee was the Nomenclature SubCommittee, which was organized in 1961 by the (US) National Research Council. The Chair of the AIPEA Nomenclature Committee is a standing member of the CMS Nomenclature Committee so that the committees are in close contact. The purpose of the AIPEA Nomenclature Committee has been to make general and specific recommendations concerning: (1) definitions of mineralogical and crystallographic clay-related terms; (2) classification and terminology …

Nomenclature of the micas

End members and species defined with permissible ranges of composition are presented for the true micas, the brittle micas and the interlayer-cation-deficient micas. The determination of the crystallochemical formula for different available chemical data is outlined, and a system of modifiers and suffixes is given to allow the expression of unusual chemical substitutions or polytypic stacking arrangements. Tables of mica synonyms, varieties, ill-defined materials and a list of names formerly or erroneously used for micas are presented. The Mica Subcommittee was appointed by the Commission on New Minerals and Mineral Names (“Commission”) of the International Mineralogical Association (IMA). The definitions and recommendations presented were approved by the Commission.

REPORT OF THE ASSOCIATION INTERNATIONALE POUR L’ÉTUDE DES ARGILES (AIPEA) NOMENCLATURE COMMITTEE FOR 2001: ORDER, DISORDER AND CRYSTALLINITY IN PHYLLOSILICATES AND THE USE OF THE “CRYSTALLINITY INDEX”

The purpose of this report is to describe the appropriate use of indices relating to crystallinity, such as the ‘crystallinity index’, the ‘Hinckley index’, the ‘Kubler index’, and the ‘Arkai index’. A ‘crystalline’ solid is defined as a solid consisting of atoms, ions or molecules packed together in a periodic arrangement. A ‘crystallinity index’ is purported to be a measure of crystallinity, although there is uncertainty about what this means (see below). This report discusses briefly the nature of order, disorder and crystallinity in phyllo-silicates and discusses why the use of a ‘crystallinity index’ should be avoided. If possible, it is suggested that indices be referred to using the name of the author who originally described the parameter, e.g. ‘Hinckley index’ or ‘Kubler index’, or in honor of a researcher who investigated the importance of the parameter extensively, e.g. ‘Arkai index’. In contrast to a crystalline solid, an ‘amorphous’ solid is one in which the constituent components are arranged randomly. However, many variations occur between the two extremes of crystalline vs. amorphous. For example, one type of amorphous material might consist simply of atoms showing no order and no periodicity. Alternatively, another amorphous material may consist of atoms arranged, for example, as groups of tetrahedra ( i.e. limited order) with each group displaced or rotated ( e.g. without periodicity) relative to another. Thus, this latter material is nearly entirely amorphous, but differs from the first. Likewise, disturbance of order and periodicity may occur in crystalline materials. The terms ‘order’ and ‘disorder’ refer to the collective nature or degree of such disturbances. Although seemingly simple notions, ‘crystalline’ and ‘amorphous’ are complex concepts. Crystalline substances may show a periodic internal structure based on direction. For example, two-dimensional periodicity is common in phyllosilicates where two adjacent sheets or layers must mesh. For example, in serpentine, …

Report of the Association Internationale pour l’Etude des Argiles (AIPEA) Nomenclature Committee for 2001: Order, disorder and crystallinity in phyllosilicates and the use of the ‘Crystallinity Index’

The purpose of this report is to describe the appropriate use of indices relating to crystallinity, such as the ‘crystallinity index’, the ‘Hinckley index’, the ‘Kubler index’, and the ‘Arkai index’. A ‘crystalline’ solid is defined as a solid consisting of atoms, ions, or molecules packed together in a periodic arrangement. A ‘crystallinity index’ is purported to be a measure of crystallinity, although there is uncertainty about what this means (see below). This report discusses briefly the nature of order, disorder and crystallinity in phyllosilicates and discusses why the use of a ‘crystallinity index’ should be avoided. If possible, it is suggested that indices be referred to using the name of the author who originally described the parameter, as in ‘Hinckley index’ or ‘Kubler index’, or in honour of a researcher who investigated the importance of the parameter extensively, as in ‘Arkai index’. In contrast to a crystalline solid, an ‘amorphous’ solid is one in which the constituent components are arranged randomly. However, many variations occur between the two extremes of crystalline vs. amorphous. For example, one type of amorphous material might consist simply of atoms showing no order and no periodicity. Alternatively, another amorphous material may consist of atoms arranged, for example, as groups of tetrahedra (i.e. limited order) with each group displaced or rotated (e.g. without periodicity) relative to another. Thus, this latter material is nearly entirely amorphous, but differs from the first. Likewise, disturbance of order and periodicity may occur in crystalline materials. The terms ‘order’ and ‘disorder’ refer to the collective nature or degree of such disturbances. Although seemingly simple notions, ‘crystalline’ and ‘amorphous’ are complex concepts. Crystalline substances may show a periodic internal structure based on direction. For example, two-dimensional periodicity is common in phyllosilicates where two adjacent sheets or layers must mesh. For example, …

Forsteritic olivine : Effect of crystallographic direction on dissolution kinetics

Abstract Directional dissolution along the three crystallographic axes of gem-quality olivine (Fo 91 ), San Carlos, Arizona was studied at pH 1 and pH 2 at 23, 50, 70, and 90°C and 1 atm. The rate constant of dissolution for olivine at pH 1 and 70°C down the a -, b -, and c -axis (based on space group Pbnm ) is 2.7 × 10 −4 , 5.6 × 10 −3 , and 8.1 × 10 −4 mm/h, respectively. At pH 2 and 70°C the dissolution rates are 1.3 × 10 −4 , 2.1 × 10 −3 , and 4.3 × 10 −4 mm/h, respectively. At 50°C and 90°C, these rates are ∼0.2 and 5 times the rates at 70°C. The much higher dissolution rate in the direction of the b -axis is attributed to preferential protonation of the oxygen atoms around the M(1) site, which would result in a higher dissolution rate of the SiO 2 -M(1) network. The activation energy of dissolution E a dis in the direction down the a -, b -, and c -axis is 114.5 ± 23 kJ/mol, 69.9 ± 8 kJ/mol, and 72.9 ± 15 kJ/mol, respectively. Because of differences in the directional E a dis , dissolution in the direction down the a -axis will become dominant at temperatures above ∼140°C. The bulk E a dis , based on the dissolution rate along the crystallographic axes, is 71.5 ± 12 kJ/mol at the temperature range of the study. Because of the larger E a dis perpendicular to the a -axis, bulk E a dis must increase with temperature. The results indicate that the weathering rate of olivine is more temperature dependent than was considered previously.

X-ray Diffraction Study of K- and Ca-Exchanged Montmorillonites in CO2 Atmospheres

Powder X-ray diffraction shows that K- and Ca-exchanged montmorillonites swell upon interacting with CO(2) at ambient temperatures, depending on their initial hydration state. K-exchanged montmorillonite swells rapidly to a maximum d(001) of ∼12.2 Å. In contrast, Ca-exchanged montmorillonite swells more slowly, but reaches a maximum d(001) of ∼15.1 Å. Reaction kinetics differ significantly between the K- and Ca-exchanged montmorillonite complexes. Expansion of K-exchanged montmorillonite samples was rapid, occurring on time scales of tens of minutes or less. The Ca-exchanged montmorillonite samples continued to expand over periods up to 42 h. Aging of both K- and Ca-exchanged montmorillonite complexes at elevated CO(2) pressure for 1-2 days resulted in greater stability when CO(2) pressure was released. The observed intercalation reactions have important consequences for carbon sequestration: (1) CO(2) absorption by swelling clays may represent a significant pathway for storage of CO(2). (2) The swelling of smectites under CO(2) pressure may have a significant impact on the permeability of caprock formations.

New gas-hydrate phase: Synthesis and stability of clay–methane hydrate intercalate

Intercalated Na-rich montmorillonite-methane hydrate was synthesized for the first time. The upper limit of stability for the intercalate in pressure and temperature is parallel to that of methane hydrate but at temperatures that are ∼0.5-1 °C lower than for methane hydrate. The low-temperature stability of the intercalate is at -11.5 ′ 3 °C at ∼40 bar, where methane and some H 2 O are expelled from the region between the silicate layers (interlayer). In contrast, methane hydrates do not dissociate at these low temperatures. We conclude that at conditions similar to where methane hydrate is stable, smectite may intercalate with methane hydrate and provide additional sinks for methane. The limitation in the stability of smectite-methane hydrate intercalate at low temperatures suggests that, if present in large quantities, it may release at decreasing temperatures sufficient methane to ameliorate a planetary cooling event.

Crystal structure of tetramethylammonium-exchanged vermiculite

Vermiculite crystals from Santa Olalla, Spain, were intercalated with tetramethylammonium (TMA) after Na saturation. The resulting TMA-vermiculite showed near perfect 3-dimensional stacking order with cell parameters of a = 5.353(1) Å, b = 9.273(2) Å, c = 13.616(6) Å, β = 97.68(3)°, and space group C2/m, which indicated a 1M polytype. Single crystal X-ray refinement (R = 0.073, wR = 0.082) located the central atom (N) of the TMA (occupancy at 0.418) and the C atom of 1 methyl group (occupancy at about 0.35). The TMA is offset from the center plane between 2 silicate layers by 1.52 Å, and the methyl group is keyed into the silicate ring of the adjacent silicate layer. This arrangement constrains the positions of the C atoms of the other methyl groups to an opposing plane parallel to the oxygen basal plane. Associated H2O is randomly located between the TMA pillars, and no scattering from these molecules was observed. The calculated height of the TMA molecule is shown to be 4.15 Å.Steric and electrostatic arguments suggesting that adjacent TMA molecules must alternate apex directions (±c) allow for a description of the local TMA arrangement. This model involves the keying of TMA molecules laterally, thereby explaining why perfect 3-dimensional stacking occurs. The offset of TMA from the center of the interlayer region produces a cavity suitable as an adsorption site for small molecules, such as benzene, which is consistent with the higher than expected adsorption of these molecules in TMA-smectites of high layer charge. This offset also explains the easy expandability of TMA-clays, since only very weak interactions occur between TMA and 1 adjacent silicate layer, thereby allowing molecules to enter the interlayer.

Summary of recommendations of nomenclature committees relevant to clay mineralogy: report of the Association Internationale pour l’Etude des Argiles (AIPEA) Nomenclature Committee for 2006

Brindley et al. (1951) reported the earliest efforts to obtain international collaboration on nomenclature and classification of clay minerals, initiated at the International Soil Congress in Amsterdam in 1950. Since then, national clay groups were formed, and they proposed various changes in nomenclature at group meetings of the International Clay Conferences. Most of the national clay groups have representation on the Nomenclature Committee of the Association Internationale pour l’Etude des Argiles (AIPEA, International Association for the Study of Clays), which was established in 1966. The precursor committee to the AIPEA Nomenclature Committee was the Nomenclature Subcommittee of the Comite International pour l’Etude des Argiles (CIPEA, International Committee for the Study of Clays). The AIPEA Nomenclature Committee has worked closely with other international groups, including the Commission on New Minerals and Mineral Names (CNMMN) of the International Mineralogical Association (IMA), which is responsible for the formal recognition of new minerals and mineral names, and the International Union of Crystallography (IUCr), which considered extensions to the nomenclature of disordered, modulated and polytype structures (Guinier et al. , 1984) published earlier by a joint committee with the IMA (Bailey, 1977). In contrast to the other national clay groups, however, The Clay Minerals Society (CMS) Nomenclature Committee, which was established in 1963 at the same time as the CMS and predates the AIPEA Nomenclature Committee, remains in existence and occasionally produces recommendations. The precursor to this committee was the Nomenclature Sub-Committee, which was organized in 1961 by the (US) National Research Council. The Chair of the AIPEA Nomenclature Committee is a standing member of the CMS Nomenclature Committee so that the committees are in close contact. The purpose of the AIPEA Nomenclature Committee has been to make general and specific recommendations concerning: (1) definitions of mineralogical and crystallographic clay-related terms; (2) classification and terminology …