Showing papers in "Reviews in Mineralogy & Geochemistry in 2001"

Oxygen Isotope Variations of Basaltic Lavas and Upper Mantle Rocks

Abstract: This chapter summarizes the oxygen isotope geochemistry of terrestrial basalts and their mantle sources, including the conceptual framework for interpreting such data and the phenomenology of known variations. In particular, the first section outlines the motivations for and first-order results of oxygen isotope studies of terrestrial and lunar basalts over the last 30 years; the second section reviews oxygen isotopic fractionations among phases relevant for studying basalts and mantle rocks; the third summarizes variations in δ^(18)O of various crustal rocks that may contribute to the petrogenesis of basalts either as subducted source components or lithospheric contaminants; and the final and longest section describes observed oxygen isotope variations of major classes of terrestrial basalts and related mantle nodules with an emphasis on data generated within the last six years using laser-based fluorination techniques. In the interests of brevity, I do not describe in detail methods for oxygen isotope analysis or changes in δ^(18)O of volcanic rocks caused by sub-solidus alteration; however, these issues are important practical considerations for anyone studying oxygen isotope compositions of basalts and interested readers are directed to the following references: analytical methods: Sharp (1990), Mattey and Macpherson (1993), and Valley et al. (1995); basalt alteration: Muehlenbachs (1986), Alt (1993), and Staudigel et al. (1995).

Fractionation of Carbon and Hydrogen Isotopes in Biosynthetic Processes

Abstract: This review is concerned with the isotopic relationships between organic compounds produced by a single organism, specifically their enrichments or depletions in 13C relative to total-biomass carbon. These relationships are biogeochemically significant because 1. An understanding of biosynthetically controlled, between-compound isotopic contrasts is required in order to judge whether plausibly related carbon skeletons found in a natural mixture might come from a single source or instead require multiple sources. 2. An understanding of compound-to-biomass differences must underlie the interpretation of isotopic differences between individual compounds and total organic matter in a natural mixture. My approach is pedagogic. The coverage is meant to be thorough, but the emphases and presentation have been chosen for readers approaching this subject as students rather than as research specialists. In common with the geochemists in my classes, many readers of this paper may not be very familiar with biochemistry and microbiology. I have not tried to explain every concept from those subjects and I have not inserted references for points that appear in standard texts in biochemistry or microbiology. Among such books, I particularly recommend the biochemistry text by Garrett and Grisham (1999) and the microbiology text by Madigan et al. (2000). The biochemistry text edited by Zubay (1998) is also particularly elegant and detailed. White (1999) has written a superb but condensed text on the physiology and biochemistry of prokaryotes. A schematic overview of the relevant processes is shown in Figure 1⇓. Plants and other autotrophs fix CO2. Animals and other heterotrophs utilize organic compounds. If the assimilated carbon is a small molecule (like CO2, CH4, or acetate), significant isotopic fractionation is likely to accompany the fixation or assimilation of C. Such fractionations establish the isotopic relationship between an organism and its carbon source. Those associated …

Biogeochemistry of Sulfur Isotopes

Abstract: Sulfur, with an atomic weight of 32.06, has four stable isotopes. By far the most abundant is 32S, representing around 95% of the total sulfur on Earth. The next most abundant isotope is 34S, followed by 33S, and finally 36S is the least abundant contributing only 0.0136% to the total (Table 1⇓). The natural abundances of sulfur isotopes, however, vary from these values as a result of biological and inorganic reactions involving the chemical transformation of sulfur compounds. For thermodynamic reasons, the relative abundance of sulfur isotopes can vary between coexisting sulfur phases. This is because lighter masses partition more of the total bond energy into vibrational rather than translational modes. Bonds with a higher vibrational energy are also more easily broken which is why lighter isotopes are generally enriched in the reaction products in chemical reactions with associated fractionation. Thus, for a nonreversible chemical reaction, as often occurs in biological systems, independent reactions may be written for the transformation of the light, L, and heavy, H, isotopes of reactant, A, to product, B (Eqns. 1 and 2). View this table: Table 1. Natural abundance ofstable sulfur isotopesa \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[A\_{H}\ {{\rightarrow}\_{}^{k\_{H}}}\ B\_{H}\] \end{document}(1) \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[A\_{L}\ {{\rightarrow}\_{}^{k\_{L}}}\ B\_{L}\] \end{document}(2) Each of these reactions has associated rate constants, kH and kL, and as described above, kH is generally less than kL, yielding an enrichment of the lighter isotope in the product. Fractionations associated with a unidirectional process are referred to as kinetic fractionations. Fractionations can also occur between two chemical species at equilibrium. The basis for equilibrium fractionations is thermodynamic and, as with kinetic fractionations, is related to mass-dependent differences in bond energies between light and heavy isotopes. The generalized isotope equilibrium between two chemical species is presented in Equation (3). \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[x\ A\_{L}\ +\ y\ B\_{H}\ {\leftrightarrow}\ x\ A\_{H}\ +\ y\ B\_{L}\] \end{document}(3) From Equation (3) an equilibrium constant, Keq, may be …

Equilibrium Oxygen, Hydrogen and Carbon Isotope Fractionation Factors Applicable to Geologic Systems

Abstract: As demonstrated by the chapters in this short course, stable isotope techniques are an important tool in almost every branch of the earth sciences. Central to many of these applications is a quantitative understanding of equilibrium isotope partitioning between substances. Indeed, it was Harold Urey’s (1947) thermodynamically based estimate of the temperature-dependence of 18O/16O fractionation between calcium carbonate and water, and a recognition of how this information might be used to determine the temperatures of ancient oceans, that launched the science of stable isotope geochemistry. The approach pioneered by Urey has since been used to estimate temperatures for a wide range of geological processes (e.g. Emiliani 1955; Anderson et al. 1971; Clayton 1986; Valley, this volume). In addition to their geothermometric applications, equilibrium fractionation data are also important in the study of fluid-rock interactions, including those associated with diagenetic, hydrothermal, and metamorphic processes (Baumgartner and Valley, this volume; Shanks, this volume). Finally, a knowledge of equilibrium fractionation is a necessary first step in evaluating isotopic disequilibrium, a widespread phenomenon that is increasingly being used to study temporal relationships in geological systems (Cole and Chakraborty, this volume). In the fifty-four years since the publication of Urey’s paper, equilibrium fractionation data have been reported for many minerals and fluids of geological interest. These data were derived from: (1) theoretical calculations following the methods developed by Urey (1947) and Bigeleisen and Mayer (1947); (2) direct laboratory experiments; (3) semi-empirical bond-strength models; and (4) measurement of fractionations in natural samples. Each of these methods has its advantages and disadvantages. However, the availability of a variety of methods for calibrating fractionation factors has led to a plethora of calibrations, not all of which are in agreement. In this chapter, we evaluate the major methods for determining fractionation factors. …

Nanoparticles in the Environment

Abstract: Nanoparticles are discrete nanometer (10−9 m)-scale assemblies of atoms. Thus, they have dimensions between those characteristic of ions (10−10 m) and those of macroscopic materials. They are interesting because the number of atoms in the particles is small enough, and a large enough fraction of them are at, or near surfaces, to significantly modify the particle’s atomic, electronic, and magnetic structures, physical and chemical properties, and reactivity relative to the bulk material. Nanoparticle surfaces themselves may be distinctive. Particles may be terminated by atomic planes or clusters that are not common, or not found, at surfaces of the bulk mineral. These, and other size-related effects will lead to modified phase stability and changes in reaction kinetics. What makes a nanoparticle a nanoparticle? Definitions of the size ranges for molecules, nanoparticles, and macroscopic solids must be compound specific. However, a useful upper limit for nanoparticles is the size at which one of its properties deviates from the value for the equivalent bulk material by an amount that is significantly larger than the error of the method used to make the measurement (a few percent). In practice, some characteristic will probably be different enough to warrant description as a “nanoparticle” if it is less than a few tens of nanometers in diameter, and perhaps less than a fraction of a micron in diameter. Because of the importance of size-dependent property changes to the materials sciences, size-property relationships have been studied in detail for some systems. For example, for semiconductors, size effects become important when the particle diameter is close to the Bohr diameter of excitons in the bulk phase. Generally, semiconductor size quantization effects (relevant for naturally occurring metal sulfides, for example) appear when particles are less than 10 nm in diameter (Vogel and Urban 1997). Definition of the …

Stable Isotopes in Seafloor Hydrothermal Systems: Vent fluids, hydrothermal deposits, hydrothermal alteration, and microbial processes

Abstract: The recognition of abundant and widespread hydrothermal activity and associated unique life-forms on the ocean floor is one of the great scientific discoveries of the latter half of the twentieth century. Studies of seafloor hydrothermal processes have led to revolutions in understanding fluid convection and the cooling of the ocean crust, the chemical and isotopic mass balance of the oceans, the origin of stratiform and statabound massive-sulfide ore-deposits, the origin of greenstones and serpentinites, and the potential importance of the subseafloor biosphere. Stable isotope geochemistry has been a critical and definitive tool from the very beginning of the modern era of seafloor exploration. Early suggestions of possible submarine hydrothermal activity date from the late 1950s when a number of investigators were debating the importance of “volcanic emanations” as a factor in the widespread occurrence of manganese nodules and other ferromanganese oxide deposits on the seafloor. Arrhenius and Bonatti (1965), in their classic paper, Vulcanism and Neptunism in the Oceans, stated the following: “The origin of authigenic minerals on the ocean floor has been extensively discussed in the past with emphasis on two major processes; precipitation from solutions originating from submarine eruptions, and slow precipitation from sea water of dissolved elements, originating from weathering of continental rocks. It is concluded that in several marine authigenic mineral systems these processes overlap.” Bostrom and Peterson (1966), in another classic, published evidence for extensive and widespread Fe-rich metalliferous sediments on the seafloor with a distribution strongly correlated with the mid-ocean ridges (Fig. 1⇓). They stated: Figure 1. Distribution of metalliferous surficial sediments, enriched in (Al+Fe+Mn)/Al, around divergent plate margin (modified after Bostrom et al. 1969). Used with permission of the American Geophysical Union. “On the very crest of the East Pacific Rise, in equatorial latitudes--particularly 12° to 16°S, the sediments are enriched in …

Crystal Structures of Natural Zeolites

Abstract: ### General aspects According to the recommended nomenclature for zeolite minerals (Coombs et al. 1998), there are more than eighty distinct zeolite species. Table 1⇓ (see Appendix below) is a listing of the zeolite minerals discussed in this chapter. Although zeolites are not as geologically abundant or widespread as many other silicate mineral groups, there is perhaps more interest in the crystal structures of zeolites than in any other mineral group, as evidenced by the number of reported crystal structure refinements (Table 2⇓). View this table: Table 1. Alphabetical list of zeolites and zeolite-like minerals covered in this chapter with their, chemical formulas, space group, cell parameters, channel description, and FD (T/1,000A3). (Channel descriptions from Meier et al. (1996); cell parameters and chemical formulas from Gottardi and Galli 1985; and new data taken from this chapter.) Meier at al. (1996) use the following symbols for channel descriptions: bold numbers represent the number of tetrahedra defining the channel, the channel free diameter is given in A, the number of stars represent the number of channels in a given direction, the connectivity of channels is given by “|” to represent connected channels or “⇔“ to represent non-connected channels. View this table: Table 2. Number of crystal structures reported in ICSD (1995) for selected mineral groups. Oxygen and silicon are the two most abundant elements in the Earth’s crust, followed by Al, Fe, Ca, Na, Mg, K. Along with H, Ba, and Sr, these are also the major elements found in most zeolite minerals. In fact, many similarities can be drawn between the feldspars, the most abundant mineral group in the Earth’s crust, and zeolites. The two most important principles in understanding zeolites (or any mineral group) are that charge balance must be maintained (i.e. the sum of the formal valence charges of the ions in the chemical formula must …

Rates and Mechanisms of Isotopic Exchange

Abstract: ### Background The proliferation of stable isotope laboratories in recent years has led to a marked increase in the routine use of stable isotope analyses in geochemical studies. This trend is likely to continue because of the development of micro-analytical techniques (e.g. laser ablation, ion microprobe, femtomole-carrier gas methods, etc.) for stable isotope analysis and the potential of these techniques to reveal the detailed sequence of thermal and fluid histories preserved in the rock record (see McKibben et al. 1998). Equilibrium isotope fractionation factors and rates of isotopic exchange form the cornerstones for the interpretation of stable isotope data from natural systems. Indeed, determination of the distribution of the stable isotopes of C-O-H-S in gases, fluids, and minerals has become a standard and extremely powerful approach in elucidating the temperatures, material fluxes, rock and fluid origins, and time scales associated with ancient and active fluid-rock interaction processes in the Earth’s crust (see Valley et al. 1986). Although the thermodynamic principles underlying isotopic fractionation behavior were developed more than fifty years ago by Urey (1947), the calibration of fractionation factors has proven to be difficult. During the last four decades, a great deal of progress has been made in determining the equilibrium fractionations of 18O/16O, D/H, 13C/12C, and 34S/32S among fluid and mineral components at high temperatures (≥400°C), both from experimental exchange studies, theoretical calculations (using vibrational spectra), semi-empirical calculations (using bond-type considerations), and empirical calibrations based on natural assemblages (see references in O’Neil 1986; Kyser 1987; Criss 1991, 1999; Chacko et al., this volume). Of these, the experimental method is the most direct because it involves the least number of a priori assumptions. Despite the utility of the equilibrium approach in quantifying the isotopic behavior in select water-rock …

Isotopic Evolution of the Biogeochemical Carbon Cycle During the Precambrian

Abstract: Carbon is highly important for our biosphere, not just because it forms organic compounds; it also creates atmospheric greenhouse gases, pH buffers in seawater, and redox buffers virtually everywhere. Carbon species can stabilize metamorphic minerals and they can affect plutonism and volcanism. These various C constituents all interact via the biogeochemical C cycle, an array of C reservoirs linked by a network of physical, chemical and biological processes. The overall C cycle actually consists of multiple nested cyclic pathways that differ with respect to some of their reservoirs and processes (Fig. 1⇓). However, all pathways ultimately pass through the hydrosphere and atmosphere, and it is this common course that unites the entire carbon cycle and allows even its most remote constituents to influence our environment and biosphere. Figure 1. Biogeochemical C cycle, showing principal C reservoirs (boxes) in the mantle, crust, oceans and atmosphere, and showing the processes (arrows) that unite these reservoirs. The range of each of these reservoir boxes along the horizontal axis gives a visual estimate of δ13C values most typical of each reservoir. The vertical bars at right indicate the timeframes within which C typically completely traverses each of the four C sub-cycles (the HAB, SED, MET and MAN sub-cycles, see text). For example, C can traverse the hydrosphere-atmosphere-biosphere (HAB) sub-cycle typically in the time scale between 0 to 1000 years. The history of the biogeochemical C cycle has been at least partially recorded in the C isotopic composition (δ13CPDB) of carbonate (δcarb) and reduced C (δorg) in ancient sedimentary and metamorphic rocks. To the extent that sedimentary rocks avoided deep burial and alteration, they have preserved information that indicates the status of the C cycle at the time of their deposition. The C cycle can be represented as an …

Occurrence of Zeolites in Sedimentary Rocks: An Overview

Abstract: Zeolites have been known since the mid-1750s, but prior to the early 1950s, most reported occurrences of zeolites were in fracture fillings and amygdules in igneous rocks, particularly basaltic lava flows. Indeed, most of the large attractive zeolite specimens in museum collections were obtained from lavas. In recent years, zeolites have been recognized as important rock-forming constituents in low-grade metamorphic rocks and in a variety of sedimentary rocks. Most zeolites in sedimentary rocks are finely crystalline, that is they occur as microscopic or submicroscopic crystals, and they are therefore of little appeal to mineral collectors; however, deposits of this type are voluminous and have great geologic significance and economic potential. Zeolites are among the most common authigenic silicate minerals that occur in sedimentary rocks, and they form in sedimentary rocks of diverse lithology, age, and depositional environment. About twenty species of zeolites have been reported from sedimentary rocks, but only eight zeolites commonly make up the major part of zeolitic rocks. These are analcime, chabazite, clinoptilolite, erionite, heulandite, laumontite, mordenite, and phillipsite. This chapter will consider chiefly the zeolites in sedimentary rocks, with emphasis on volcaniclastic deposits, which contain the largest concentrations of zeolites. The occurrence of zeolites in lava flows is mentioned only briefly. Journal articles on the occurrence and origin of natural zeolites have multiplied at a rapid rate since the Mineralogy and Geology of Natural Zeolites was first published in 1977 as Volume 4 of the Mineralogical Society of America’s Reviews in Mineralogy . The present review will highlight areas of more recent research on the occurrence and origin of zeolites and some of the coexisting minerals. A wide variety of zeolites has been identified in sedimentary deposits, with the most common being clinoptilolite, analcime, heulandite, laumontite, and phillipsite. Less abundant zeolites include chabazite, erionite, mordenite, natrolite …

Stable Isotope Thermometry at High Temperatures

Abstract: Determination of accurate temperatures for geological events has been the grail of stable isotope geochemistry since the seminal 1947 paper by Urey. In theory, this should be simple. Calibrated mineral pairs are common, analysis is rapid, and there is no significant pressure correction. However, in spite of widespread application, the promise of reliable thermometry has been elusive. Stable isotope temperatures in metamorphic and igneous rocks are often controversial; is the fractionation between two phases a thermometer, speedometer (rate dependant), hygrometer (P(H2O)-dependant), or chimera? A number of factors have contributed to this uncertainty including: incomplete and sometimes conflicting calibration of isotope fractionation factors; limited understanding of the kinetics of mineral exchange; and the lack of microanalytical techniques. This situation has improved dramatically over the past decade, permitting reliable and detailed thermal histories to be inferred. In a landmark paper, Bottinga and Javoy (1975) empirically calibrated the oxygen isotope fractionation factors among ten rock-forming minerals at T > 500°C. Their compilation shows that 84% of analyzed samples contain at least three minerals meeting a concordance test for equilibrium. They concluded “the great majority of igneous and metamorphic rocks …. has conserved a state of oxygen isotope exchange equilibrium.” If correct, this bodes well for thermometry. However, this conclusion was contested by Deines (1977) who critically examined the existing data and concluded that “less than half of the rocks analyzed to date would yield concordant 18O-derived temperatures.” While seeming irreconcilable, both conclusions are based on fact. All rocks contain some degree of disequilibrium, but many also preserve a thermometric record. It is the purpose of this review to discuss the new strategies for reliable isotope thermometry and to explore disequilibrium processes so they may be recognized and properly interpreted. The organization of this paper will be to discuss the assumptions …

Geochemical Stability of Natural Zeolites

Abstract: Zeolites are used in numerous agricultural, commercial, and environmental applications (e.g. as soil conditioners and fertilizers, and as adsorbents for ammonia, heavy metals, nuclear and organic wastes). It is important to understand their stability to insure their persistence and effectiveness in these applications. An analysis of the occurrence of natural zeolites provides basic data on conditions favorable for zeolite stability and formation. All such environments have neutral to alkaline waters and, with few exceptions, are associated with low-temperature (<300°C) alteration of highly reactive volcanic rocks containing natural glasses. The principal exceptions are certain deep sedimentary sequences, sometimes associated with petroleum maturation where volcanic ash falls are absent, and deep-sea sediments where biogenic opal may be the highly reactive phase. Since initial recognition of the zeolite facies in diagenetic alteration (Coombs et al. 1959), investigators have struggled to develop a quantitative basis for defining zeolite stability fields by development of both the thermodynamic relations and kinetic factors governing zeolite formation. An additional motivation for study in the United States and elsewhere is the occurrence (and use) of zeolites at potential sites for disposing of high-level radioactive waste in underground repositories. Regulatory requirements for a high-level radioactive waste repository, reflecting public concerns over the integrity of subsurface disposal facilities, require unprecedented quantitative predictions of the physical-chemical response of zeolites to heat generated during radioactive decay and to waste-rock interactions over a time period exceeding tens of thousands of years. In light of such requirements, investigators are taking a new look at the thermodynamic and kinetic factors affecting zeolitization. The geochemical conditions that result in zeolite formation have been outlined in numerous studies (e.g. Hay 1966, 1978; Iijima 1978, Surdam and Sheppard 1978, Sheppard and Hay, this volume; Hay and Sheppard, this volume). Aqueous silica activity, cation concentrations, and …

Stable Isotope Transport and Contact Metamorphic Fluid Flow

Abstract: Stable isotopes are a powerful tool for deciphering the fluid histories of metamorphic terranes. The nature of fluid flow, fluid sources, and fluid fluxes can be delineated in well-constrained studies. Observed isotopic gradients in metamorphic rocks and minerals can thus shed light on many processes involved in mass-transport including diffusion, recrystallization, fluid infiltration, volatilization, metasomatism, and heat flow. Modeling of fluid flow and mineral exchange kinetics offers greatly enhanced understanding of metamorphic processes that can be tested and refined by application of new micro-analytical techniques. This review will concentrate on the principles of stable isotope fluid-rock interaction with an emphasis on fluid-rock interaction and fluid flow in contact metamorphism. Earlier reviews discuss some aspects of regional metamorphism and hydrothermal systems (Valley 1986; Kerrich 1987; Nabelek 1991; Young 1995; Ferry and Gerdes 1998; Bowman 1998). Isotopic studies are especially useful for defining the scale of fluid migration. The intensity of interaction between fluids and the minerals in rocks can be assessed. During metamorphism, the scale of isotopic exchange can vary from less than a micrometer to over 10 kilometers. Many fluid-driven processes are characterized by the degree to which fluid flow is concentrated into zones of high permeability. Thus, the definition of two end-member situations is useful. The flow of a pervasive fluid is distributed throughout the pores in a rock. Pervasive flow can be along grain boundaries or fine-scale crack networks and the effect is to homogenize the chemical potential of all components, including stable isotopes, at a macroscopic scale. In contrast, the flow of a channeled fluid is along vein systems, shear zones or other channelways such as rock contacts or more permeable lithologic units. Channeled flow leads to local chemical heterogeneity, allowing some rocks to remain unaffected while others are extensively infiltrated …

Cation-Exchange Properties of Natural Zeolites

Abstract: Zeolite minerals are crystalline, hydrated aluminosilicates of alkali and alkaline earth cations characterized by an ability to hydrate/dehydrate reversibly and to exchange some of their constituent cations with aqueous solutions, both without a major change in structure. Because of their ion-exchange, adsorption, and molecular sieve properties, as well as their geographically widespread abundance, zeolite minerals have generated worldwide interest for use in a broad range of applications. Examples of these applications are discussed in other chapters of this book. Of particular interest in this chapter are the cation-exchange properties of zeolite minerals. Due to the favorable ion-exchange selectivity of natural zeolites for certain cations, such as Cs+, Sr2+, and NH4+, these minerals have been studied for potential use in the treatment of nuclear wastewaters (Howden and Pilot 1984; Baxter and Berghauser 1986; Robinson et al. 1995; Pansini 1996), municipal and industrial wastewaters (Kallo 1995; Pansini 1996), and acid mine drainage waters (Bremner and Schultze 1995; Zamzow and Schultze 1995). Natural zeolites have also been studied for potential use in the remediation of sites contaminated with fission products such as 90Sr and 135,137Cs (Leppert 1988; Valcke et al. 1997a; Valcke et al. 1997b) and in the remediation of soils contaminated with heavy metals (Ming and Allen, this volume). Additional interest resulted from the potential siting of a high-level nuclear waste repository at Yucca Mountain, Nevada, which is underlain by diagenetically altered, zeolite-rich (clinoptilolite, heulandite, and mordenite) rhyolitic tuffs (Broxton et al. 1986; Broxton et al. 1987) that could serve as barriers to radionuclide migration to the accessible environment. Zeolites consist of three-dimensional frameworks of (Si,Al)O4 tetrahedra where all oxygen ions of each tetrahedron are shared with adjacent tetrahedra. The presence of Al3+ …

Applications of Natural Zeolites in Water and Wastewater Treatment

Abstract: The world is faced with increasing demands for high-quality drinking water and for removal of contaminants from municipal, agricultural, and industrial wastewaters. Treatment is required to obtain drinking water from most natural resources as well as from wastewaters with varying amounts of impurities. These impurities may occur in a variety of forms including large particles such as microorganisms or suspended solids or as dissolved or colloidal inorganic and organic substances. This chapter provides an overview of the use of natural zeolites in removal of impurities from water or wastewater (Murphy et al. 1978, Tarasevich 1994, Kallo 1995). Most technologies using natural zeolites for water purification are based on the unique cation-exchange behavior of zeolites through which dissolved cations can be removed from water by exchanging with cations on a zeolite’s exchange sites (see Pabalan and Bertetti, this volume). The most common cation in waters affecting human and animal health is NH4+. It can be removed by exchanging with biologically acceptable cations such as Na+, K+, Mg2+, Ca2+ or H+ residing on the exchange sites of the zeolite. Fortunately, many natural zeolites (e.g. clinoptilolite, mordenite, phillipsite, chabazite) are selective for NH4+ ( vide infra ), meaning that they will exchange NH4+ even in the presence of larger amounts of competing cations. Clinoptilolite and mordenite are also selective for transition metals (e.g. Cu2+, Ag+, Zn2+, Cd2+, Hg2+, Pb2+, Cr3+, Mo2+, Mn2+, Co2+, Ni2+), which are often present in industrial waters and can be very toxic even in concentration as low as several mg/L. As emphasized in discussions of radioactive waste treatments, both clinoptilolite and mordenite …

The Crystal Chemistry of Zeolites

Abstract: ### Definition of zeolite This chapter discusses the crystal chemistry, emphasizing observed chemical variations, for those zeolites that completely fulfill the requirements of Smith (1963) for a zeolite. These requirements include: (a) a three-dimensional framework of tetrahedra occupied more than 50% by Si and Al; (b) an “open” structure with a framework density (i.e. number of tetrahedral atoms per 1000 A3) lower than 20 (Brunner and Meier 1989) and hence enclosing cavities connected by windows larger than regular six-membered rings; and (c) an extraframework content represented by cations and water molecules. Thus, this chapter will not deal with those phases which are commonly classified as feldspathoids (leucite, pollucite) and those that can be classified as beryllo-phosphates (pahasapaite, weinebeneite), beryllo-silicates (chiavennite, hsianghualite), or zinc-silicates (gaultite). The requirements of Smith (1963) account for the characteristic properties of zeolites (molecular sieve, reversible dehydration, cation exchange), and although for some zeolite species, cation exchange is incomplete or is not yet reported, the presence of large windows (requisite b) reasonably assures its feasibility. Using the above criteria, all minerals known to date which can be classified as zeolites are listed in Table 1⇓. View this table: Table 1. Schematic chemical formulae of natural zeolites. STC = Structure Type Code; Ra = Average Si/(Si+Al+Be); Rr = Range of Si/(Si+Al+Be); DEC = Dominant Extraframework Cations; SEC = Subordinate Extraframework Cations. Italic: Be-bearing species. Underlined: species with an “interrupted framework” In the general formula MxDy[Alx+2ySin-(x+2y)O2n]· m H2O, where M are monovalent and D are divalent cations, it is possible to distinguish two parts, which although very different, are mutually dependent and form a homogeneous complex endowed with exclusive chemico-physical properties. The portion in square brackets represents the tetrahedral framework and is characterized by an overall negative charge which increases as …

Use of Natural Zeolites in Agronomy, Horticulture and Environmental Soil Remediation

Abstract: “In the next century, it is possible that a huge industry will develop based on natural zeolites. Soil conditioning by zeolites might lead to greater agricultural production. Control of toxic materials in waste water by zeolites might rescue some stressed aquasystems. There just might be gold for geochemists in them thar zeolite beds.” J. V. Smith (1988) The use of natural zeolites to improve plant productivity or as a remediation agent in environmental protection has the potential of becoming a “huge” industry as pointed out in the above quote by Smith (1988). This potential industry is based on the unique chemical and physical properties of natural zeolites (e.g. high cation-exchange capacities, cation selectivity, molecular sieving) and their widespread occurrence in sedimentary deposits derived from volcanic materials. A variety of potential applications have been examined for natural zeolites, including use as soil conditioners, slow-release fertilizers, soilless substrates, carriers for insecticides and pesticides, and remediation agents in contaminated soils. However, although numerous applications have been suggested or examined, today there are only a few commercial markets for natural zeolites in the horticultural, agronomic, and environmental protection industries. Allen and Ming (1995) suggested that there may be several reasons that the commercial use of natural zeolites has been slow to develop, including (1) the lack of studies that focus on deriving the economic benefits of zeolite applications; (2) the need to develop products and formulations that meet a specific agronomic, horticultural, or environmental use, instead of a one-size-fits-all approach; (3) the need to fully characterize the zeolite or zeolite-containing material before it is utilized; and (4) the lack of sound scientific research to support the proposed uses of zeolites. We agree with J.V. Smith that the potential applications for natural zeolites are huge, provided the proper research is conducted to fully use …

Thermal Behavior of Natural Zeolites

Abstract: The open framework structures of zeolites, containing variable amounts of extra-framework cations and water molecules, are very responsive to changes in temperature and/or water-vapor pressure. Several coupled changes occur in water content and structure whenever a zeolite is subjected to a change in environment. The structural changes include modifications in the unit-cell size and geometry, movement of extraframework cations, and even statistical breakage of the Al-Si framework. The water content in some zeolites is a smoothly varying function of temperature and water-vapor pressure, whereas in others there appear to be distinct transitions between different hydration levels. The response of zeolites to changes in temperature and/or water-vapor pressure is thus a very important aspect of their behavior and has a bearing on subjects ranging from their industrial applications to their identification. For example, numerous zeolites are used in gas adsorption, as selective catalysts, and as molecular sieves, and a detailed understanding of their short-term (e.g. overnight) thermal behavior and appropriate activation temperatures is crucial. Short-term thermal behavior has also been suggested as a means to distinguish between similar zeolites, such as clinoptilolite from heulandite (Mumpton 1960) and barrerite from stellerite (Passaglia 1980). In addition, de’Gennaro and Colella (1989) showed that the zeolite content in mixtures such as zeolitic tuffs can be determined through the details of the bulk-sample water-vapor desorption behavior. In contrast, other applications (e.g. the performance of clinoptilolite in a high-level radioactive waste repository) require that the long-term (102 to 105 years) behavior of these minerals under elevated-temperature conditions be understood. Because many thermal reactions of interest are at least partially kinetically limited, effects that may not be important during short-term heating can become increasingly important during long-term heating. In some instances, long-term heating experiments show results very different from those of shorter duration (e.g. Bish 1990a …

Molecular Simulations of Liquid and Supercritical Water: Thermodynamics, Structure, and Hydrogen Bonding

Abstract: Water is a truly unique substance in many respects. It is the only chemical compound that naturally occurs in all three physical states (solid, liquid and vapor) under the thermodynamic conditions typical to the Earth’s surface. It plays the principal role in virtually any significant geological and biological processes on our planet. Its outstanding properties as a solvent and its general abundance almost everywhere on the Earth’s surface has made it also an integral part of many technological processes since the very beginning of the human civilization. Aqueous fluids are crucial for the transport and enrichment of ore-forming constituents (Barnes 1997; Planetary Fluids 1990). Quantitative analysis of hydrothermal and metamorphic processes requires information on the physical-chemical, thermodynamic and transport properties of the fluid phases involved (Helgeson 1979, 1981; Sverjensky 1987; Eugster and Baumgartner 1987; Seward and Barnes 1997). These processes encompass a broad range of pressure and temperature conditions and, therefore, detailed understanding of the pressure and temperature dependencies of density, heat capacity, viscosity, diffusivities, and other related properties is necessary in order to develop realistic models of fluid behavior or fluid-mineral interactions. Aqueous fluids under high-pressure, high-temperature conditions near and above the critical point of water ( P = 22.1 MPa and T = 647 K) are especially important in a variety of geochemical processes. Due to the large compressibility of supercritical fluid, small changes in pressure can produce very substantial changes in density, which, in turn, affect diffusivity, viscosity, dielectric, and solvation properties, thus dramatically influencing the kinetics and mechanisms of chemical reactions in water. Models of hydrothermal convection suggest that the near-critical conditions provide an optimal convective behavior due to unique combination of thermodynamic and transport properties in this region of the phase diagram of water (Norton 1984; Jupp and Schultz 2000 …

Thermochemistry of Nanomaterials

Abstract: The term “nanoparticle” or “nanomaterial” is somewhat difficult to define rigorously. A nanoparticle has dimensions somewhere in the nanometer regime, that is, a diameter of 1 to 100 nm. Thus nanoparticles span the range from clusters of atoms in solution at the small end to colloidal particles at the large end. Nanoparticles may be amorphous or consist of only a few unit cells of crystalline material. A very large fraction of their atoms are near the surface, see Figure 1⇓. Nanoparticles may be surrounded by vacuum, a gaseous atmosphere, water, or other fluid. In the natural environment, nanoparticles are generally heavily hydrated. Figure 1. Fraction of atoms within 0.5 nm of the surface of a nanoparticle as a function of its diameter. [Used by permission of the editor of Materials Research Society Symp Proc , from Navrotsky (1997), Fig. 3, p. 10.] A nanomaterial can be loosely defined to be any material containing heterogeneity at the nanoscale in one or more dimensions. In the broadest sense, then, the following are nanomaterials: phase-separated glasses or crystals with domains in the nanoregime, zeolites and mesoporous materials with pores of nanometer dimensions, clays with nanometer sized alternations of aluminosilicate layers and interlayer hydrated cations, and nanoscale leach layers at the mineral-water interface. A broad definition in the sense above emphasizes the commonality of phenomena at the nanoscale. In essence “if it quacks like a nanomaterial, it is one.” A nanomaterial is any state of condensed matter whose properties diverge significantly from those of the bulk or of molecules by the emergence of new phenomena not seen at smaller or larger scales. Such properties are related to nanoscale heterogeneity created by pervasive surfaces, interfaces, chemical variability, or pores. The exact size at which this happens depends both on the system and the property …

Molecular Modeling in Mineralogy and Geochemistry

Abstract: “A theory is something nobody believes, except the person who made it. An experiment is something everybody believes, except the person who made it.” Attributed to Albert Einstein “A theory has only the alternative of being right or wrong. A model has a third possibility: it may be right, but irrelevant.” Manfred Eigen At what underlying fundamental level of understanding does geosciences research need to attain in order to evaluate the complex processes that control the weathering rate of silicate minerals? To investigate the formation of ore deposits and oil reservoirs, or the leaching of mine tailings into watersheds and the eventual contamination of groundwater? To predict the crustal deformation of long-term underground waste storage sites, or the stability of lower mantle phases and their effect on seismic signals? Or, for that matter, to examine tectonic uplift and cooling rates associated with orogenies? These and numerous other examples from mineralogy and geochemistry often require an understanding of atomic-level processes to identify the fundamental properties and mechanisms that control the thermodynamics and kinetics of Earth materials. Molecular models are often invoked to supplement field observations, experimental measurements, and spectroscopy. Theoretical methods provide a powerful complement for the experimentalist, especially with recent trends in which atomic-scale measurements are being made at synchrotron and other high-energy source facilities throughout the world. Such analytical methods and facilities have matured to such an extent that mineralogists and geochemists routinely probe Earth materials to evaluate bulk, surface, defect, intergranular, compositional, isotopic, long-range, local, order-disorder, electronic, and magnetic structures. Molecular modeling theory provides a means to help interpret the field and experimental observation, and to discriminate among various competing models to explain the macroscopic observation. And ultimately, molecular modeling provides the basis for prediction to further test the validity of the scientific hypothesis. This is especially significant …

Isotopic Biogeochemistry of Marine Organic Carbon

Abstract: The ocean accounts for over 90% of the active pools of carbon on the Earth’s surface, with over 95% of marine carbon in the form of dissolved inorganic carbon (DIC) (Hedges and Keil 1995). Organic carbon dissolved in the ocean, suspended as particles or cells, and accumulating in sediments together constitute the other significant fractions of marine carbon, with organic carbon in the water column similar in quantity to the current atmospheric inventory of carbon dioxide. Isotopic partitioning among various inorganic and organic carbon phases reflects biological, physical and chemical processes, and the resulting fractionations are important tools in the study of modern and ancient carbon cycling. The focus of this review is on the isotopic geochemistry of marine organic carbon. It will begin by setting the stage with the isotopic patterns of DIC in the modern oceans. As will be discussed below, the distribution of inorganic carbon and related nutrient concentrations as well as DIC isotopic compositions are important influences on the quantity and isotopic character of organic carbon produced in marine surface waters. The remainder of the review will discuss isotope fractionation associated with the production and preservation of marine organic carbon. The combination of organic matter composition and 13C content is a potentially powerful approach for addressing the nature and pace of ecological and environmental change both in the modern and ancient ocean. This work reviews biogeochemical processes that generate, transform and ultimately preserve such signatures in marine sediments. The first truly global measurements of DIC δ13C values were produced as a result of the Geochemical Ocean Sections Study (GEOSECS). The resulting data were published in a series of articles by Kroopnick and colleagues (Kroopnick et al. 1977; Kroopnick 1980, 1985) and summarized by Takahashi et al. (1980, 1981). A striking outcome of this …

Oxygen- and Hydrogen-Isotopic Ratios of Water in Precipitation: Beyond Paleothermometry

Abstract: Paleoclimatologists face a dilemma. No sedimentary proxy is a pure recorder of quantitative climate information. Yet climate modelers and policy-makers increasingly seek quantitative comparisons between instrumentally documented, possibly anthropogenic, climate changes and those produced naturally in the past. In the second edition of his influential book, Bradley (1999, p. 6) discussed the calibration of proxy records to learn past climate changes: “Calibration involves using modern climatic records and proxy materials to understand how, and to what extent, proxy materials are climate-dependent. It is assumed that the modern relationships observed have operated, unchanged, throughout the period of interest (the principle of uniformitarianism).” In other words, one relates the characteristics of sediment to climate at different places for one time, or at a place for short times, and then uses that relation plus characteristics of older sediments to estimate the climatic conditions that produced those sedimentary characteristics. Bradley (1999) then extensively discussed the difficulties in applying this methodology in a complex world with imperfect recorders; nonetheless, the goal of using calibrated proxies for quantitative as well as qualitative paleoclimatic reconstruction is clear. A prominent recent use of calibrated paleoclimatic data is the assessment of whether the probably-anthropogenic warming of the latter 20th century moved beyond the band of natural variability of the prevailing climate. Bradley (2000) combined recent instrumental records with several longer proxy-based reconstructions of surface temperature including that of Mann et al. (1999). Based on this composite data set, Bradley (2000) argued that “temperatures in the late 20th century were unique in the context of the entire millennium”. The proxy records were primarily based on tree-ring data, but included isotopic and major-element geochemistry of corals, and occurrence of melt layers and isotopic ratios of water in ice cores. However, Broecker (2001) questioned the basis for the reconstruction of …

Zeolites in Closed Hydrologic Systems

Abstract: Zeolites were first described from vugs and fissures in basaltic flows in the mid-eighteenth century (Cronstedt 1756), and they are now known to be widespread in a variety of geological environments. More zeolite species occur in vesicles and fractures of basaltic rocks than in any other geologic setting. However, zeolites from sedimentary rocks, in particular, represent the most important occurrences both in terms of aerial extent of deposits and in terms of the abundance of certain zeolite species. The introduction of new analytical techniques in the latter part of the 20th century provided a significant stimulus to zeolite research; these techniques allowed identification of large quantities of zeolites in widespread deposits of sedimentary rocks and, in particular, in sediments from saline, alkaline lakes of the western United States (Sheppard and Gude 1968, 1969a, 1973). Based on geological and hydrologic environments, zeolite occurrences in sedimentary rocks can be classified in the following framework: (a) saline, alkaline lakes; (b) alkaline soils and land surfaces; (c) deep-sea sediments; (d) open hydrologic systems; (e) as products of hydrothermal alteration; and (f) burial diagenetic or low-metamorphic environments. From a broader perspective, zeolite deposits can be classified into two main groups, namely closed hydrologic systems and open hydrologic systems. The work of Sheppard and Gude (1968, 1969a, 1973) and later Surdam (1977), discussing not only the mineralogy of the deposits but also the geology, hydrology, and chemistry of the depositional basins, represent milestones in the study of closed hydrologic system formation of zeolites. Surdam (1977) considered closed hydrologic basins in two different tectonic settings: (a) block-faulted regions in arid and semiarid regions; and (b) trough valleys associated with rifting. Examples of the first setting are the closed lakes of the Basin and Range province of the western United States whereas the …

Formation of Zeolites in Open Hydrologic Systems

Abstract: In contrast to those deposits formed by the alteration of volcanic ash in saline, alkaline lakes discussed in the chapter by Hay and Sheppard (this volume), large volumes of tuffaceous sediments around the world have been transformed to zeolites and other authigenic silicate minerals by the action of percolating water in open hydrologic systems. These include systems that have experienced significant chemical and hydrologic exchanges with the surrounding environment. Tephra sequences exposed to open-system alteration commonly show a vertical zonation of zeolites and other authigenic minerals that reflects the chemical changes in meteoric water moving through the system. Flow in an open hydrologic system can either be downward or have a downward component where meteoric water enters the system, resulting in a vertical or nearly vertical zonation of water composition and authigenic minerals. The original pyroclastic materials of tuffaceous sediments may have been laid down in the sea close to the volcanic sources, air-laid onto the land surface, or reworked into fluviatile and freshwater lacustrine environments. Open-system zeolite deposits are most common in nonmarine rocks, although many are known in sediments that were deposited in shallow marine environments. Zeolite deposits of the open-system type are commonly several hundred meters thick and can be traced laterally for several tens of kilometers. Many examples of zeolite deposits that formed from land-laid tephra have been recognized in the western United States, but most of the large marine deposits are in Japan and in southern and southeastern Europe. Because of their relatively large and commonly discontinuous areal extent, open-system deposits have not been studied in as much detail as some other types of zeolite deposits in sedimentary rocks; however, studies of several key areas have provided a sound basis for the current understanding of this type of zeolite body. Zeolitic alteration can take place …

Use of Zeolitic Tuff in the Building Industry

Abstract: Zeolite-rich volcanic tuffs are widely distributed in almost every country of the world, where they are present in low-, medium-, or high-grade million-ton deposits. Even though the formation of the zeolite minerals may have followed different genetic paths, the zeolitic rocks have in common a matrix of finely crystalline zeolite that cements the other nonzeolitic particles and is responsible for the overall mechanical properties of the material. Zeolitic tuffs have been employed since pre-historic times in construction, mostly as dimension stone. This use is still the most common of natural zeolites in the building industry, although other applications have recently come to the forefront, such as lightweight aggregate or as additives for manufacturing blended cements. Given the fact that much of this material is excavated and used locally and that the market demand is strongly affected by the trends of the building industry, estimates of the worldwide zeolitic tuff production for construction purposes are difficult to make. In Italy, where the use of zeolitic tuff as dimension stone is commonplace, about 75 quarries were reported in operation in 1992 with total production of about 3 x 106 tons per year (Aiello 1995). More recently, this production has decreased, due to the crisis of the building industry, and in 1998 it amounted to about 1.5 × 106 tons per year. In Japan, the production of tuff as dimension stone is currently about 4 × 105 tons per year (N. Kuchitsu, National Research Institute of Cultural Properties, Tokyo, Japan, pers. comm., 1996). Considering that zeolitic tuff is used as dimension stone in many other countries as well, e.g. Bulgaria, Cuba, Germany, Greece, Hungary, Mexico, Romania, and Turkey, the current worldwide zeolitic tuff consumption as dimension stone is about 3 × 106 tons per year. Information is even more …

Structure, Aggregation and Characterization of Nanoparticles

Abstract: ### Structural aspects of natural nanomaterials A large number of mineral species occur only as micron-sized and smaller crystallites. This includes most of the iron and manganese oxyhydroxide minerals, and other species whose formation processes and growth conditions limit ultimate size. Microscopic investigation of these species generally reveals sub-micron structure down to the nanometer level, including evidence of aggregation, agglomeration and assembly of nanometer units into larger crystals and clots. The bulk of studies in the literature dealing with nanoparticle structure and growth deal with metals, silicon, and other semiconductor materials. A great deal of attention has been given to the electronic properties of such solids, owing to both new commercial applications and new fundamental physics and chemistry tied to this area. Most applicable mineralogical or geochemical studies have not addressed the same issues, instead being more concerned with relatively bulk chemical properties. Very little has been done to understand how natural nanoparticulates (and related types of natural nanomaterials) form, how their microstructure is related to the growth process, and how their structure varies from larger crystallites or bulk material of the same composition. Magnetic and electronic properties of natural nanomaterials are similarly understudied. In this chapter aspects of nucleation, aggregation and growth processes that give rise to specific microstructures and forms of nanomaterials are considered. Next the way in which the surface structure of nanoparticulates may differ from the interior, and how physical structure may be modified by reduced particle size is examined. The various techniques by which nanoparticle structure, size, microstructure, shape and size distribution are determined are then considered with examples. Finally some of the outstanding problems associated with nanoparticle structure and growth are identified, emphasizing natural processes and compositions. ### Definitions Naturally occurring nanomaterials exist in a variety of complex forms. In this chapter a short set of definitions will be stated for clarity. …

Aqueous Aluminum Polynuclear Complexes and Nanoclusters: A Review

Abstract: Most undergraduate students of aqueous geochemistry are told that polynuclear aqueous complexes can largely be ignored because they form only from concentrated metal solutions that are rare at the Earth’s surface. However, these polynuclear complexes can serve as models for more-complicated surface structures and are the precursors to nanometric and colloidal solids and solutes. There are many reasons why polynuclear complexes should be foremost in the minds of geochemists, and particularly those geochemists who are interested in molecular information and reaction pathways: 1. Polynuclear complexes contain many of the structural features that are present at mineral surfaces, including a shell of structured water molecules. Because aqueous nanoclusters tumble rapidly in an aqueous solution, one can use solution NMR spectroscopy to determine the structure and the atomic dynamics in these clusters in ways that are impossible for mineral surfaces. 2. Some polynuclear complexes are metastable for long periods of time and may represent an important vector for the dispersal of metal contaminants from hazardous waste. The chemical conditions found in many polluted soils: high metal concentrations, elevated temperatures, and either highly acidic or highly alkaline solutions with a large pH-gradient, are needed to synthesize many polynuclear complexes. It is easy to make a solution that is 5 M in dissolved aluminum at 4 < pH < 6, composed of nanometer-sized clusters that are stable for months or years. 3. Polynuclear complexes lie at the core of many biomolecules, including metalloproteins such as ferritin and enzymes such as nitrogenase. Recent work has suggested that they are present in natural waters (e.g., Rozan et al. 2000) and serve as nuclei for crystal growth. 4. Aqueous clusters are sufficiently small that they can serve as experimental models for ab initio computer simulations that relate bonding to reactivity. In this chapter we discuss polynuclear complexes of aluminum. There is …

Stable Isotope Variations in Extraterrestrial Materials

Abstract: The materials of the planets and the small bodies of the solar system contain a rich record of stable isotope variations in the light elements. As in terrestrial isotope geochemistry, this record reflects physical and chemical processes involving isotopic mixing among different reservoirs as well as fractionations arising in chemical reactions. The processes that influence the isotopic records of extraterrestrial materials range widely in environmental conditions from very high-energy events such as formation of refractory inclusions and chondrules by evaporation, condensation and melting in the solar nebula to lower temperature fluid-rock interactions in asteroids and planets. In addition, however, stable isotope cosmochemistry must consider issues that are beyond the scope of isotope geochemistry. For example, in the terrestrial sphere one may assume the existence of an isotopic reservoir that was originally homogenized during planet formation and the actual isotope compositions of the bulk earth do not need to be known in order to study the differences in stable isotope compositions that have been generated subsequently by various geochemical processes. This assumption of homogenization cannot be made for extraterrestrial samples, and in fact stable isotopes in meteorites preserve some of the most dramatic evidence for the incomplete nature of the mixing of distinct presolar materials during formation of the solar system. Such ‘isotopic anomalies’ are present in the isotopic distributions of H, C, N, and O on all spatial scales—from microscopic zoning in certain meteoritic minerals to the bulk compositions of asteroids and planets. Thus, some of the isotopic heterogeneities of ‘primitive’ solar system materials represent vestiges of primordial differences that could not be fully erased during the processing of presolar materials. In other cases, isotopic heterogeneities reflect the preservation of unique clues to processes occurring during formation of the solar system and planetary accretion, including early ‘geologic activity’ on planetesimals …

Clinoptilolite-Heulandite Nomenclature

Abstract: Heulandite was first named in 1822 for the English mineral collector, J. H. Heuland (see Dana 1914, p. 574–576). Although it is typically found as macroscopic (commonly 0.2–2 cm in size) crystals in cavities in mafic igneous rocks and is volumetrically minor on the Earth’s surface, heulandite also occurs in larger amounts in some sedimentary deposits, often in association with clinoptilolite. Due to the large size of typical heulandite crystals, its chemical composition and crystallographic and optical properties were easily characterized. Mineralogists recognized early that heulandite is monoclinic and that heating changes its optical properties in a predictable manner (Slawson 1925). Unlike heulandite, the mineral known today as clinoptilolite typically occurs as microscopic crystals, commonly 2–20 μm in size and commonly intimately admixed with other fine-grained minerals. Although clinoptilolite is known today as the most common natural zeolite, occurring in large amounts (millions of tons) in altered volcanic tuffs and saline, alkaline-lake deposits, it is generally mentioned only in passing in beginning mineralogy texts. Clinoptilolite was not described as a distinct mineral species until 1932 (Schaller 1932). Prior to that time, the platy material described by Pirsson (1890) in amygdules in weathered basalt from the Hoodoo Mountains, Wyoming, had been classified as “mordenite,” based primarily on its chemical similarity with mordenite from Nova Scotia. In spite of the chemical similarities, Pirsson did recognize the crystallographic similarity between the Wyoming “mordenite” and heulandite. Dana’s sixth edition (1914, p. 572–573) lists both ptilolite and mordenite as members of the mordenite group. Ptilolite (which we now recognize as mordenite) is listed by Dana as commonly occurring in aggregates of needles having parallel extinction, but “mordenite” is reported by Dana to be monoclinic, having a form closely approximating that of heulandite. Schaller (1932) proposed the name clino ptilolite based on the chemical …