Geology topics

J. Srodon

Publications and source records attributed to J. Srodon.

8 recordsLinked to original sources

USGS2024

Chemistry of illite/smectite and end-member illite

Chemical data from three different series of diagenetic illite/smectites (I/S), analyzed statistically by two regresion techniques, indicate that the content of fixed-K per illite layer is not constant, but ranges from ∼0.55 per O 10 (OH) 2 for illite layers in randomly interstratified I/S (R=0; > 50% smectite layers) to ∼1.0 per O 10 (OH) 2 for illite layers formed in ordered I/S (R>0; <50% smectite layers). By extrapolation of the experimental data, the following chemical characteristics were obtained for end-member illite derived from the alteration of smectite in bentonite: average fixed-K per illite layer = 0.75 per O 10 (OH) 2 ; total charge = about −0.8; cation-exchange capacity = 15 meq/100 g; surface area (EGME) = 150 m 2 /g.

Clays and Clay Minerals↗

USGS2003

Comment on "Evaluation of X-ray diffraction methods for determining the crystal growth mechanisms of clay minerals in mudstones, shales and slates," by L. N. Warr and D. R. Peacor

A recent paper by Warr and Peacor (2002) suggested that our use of the Bertaut-Warren-Averbach technique (MudMaster computer program) for studying changes in crystallite thickness distributions (CTDs) of clay minerals during diagenesis and very low-grade metamorphism is not reliable because it is dependent on many variables which can not be fully controlled. Furthermore, the authors implied that the measured shapes of CTDs cannot be used with confidence to deduce crystal growth mechanisms and histories for clays, based on our CTD simulation approach (using the Galoper computer program). We disagree with both points, and show that the techniques are powerful, reliable and useful for studying clay mineral alteration in rocks. ?? 2003 Schweiz. Mineral. Petrogr. Ges.

Schweizerische Mineralogische und Petrographische ↗

USGS2002

Interpretation of K-Ar dates of illitic clays from sedimentary rocks aided by modeling

K-Ar dates of illitic clays from sedimentary rocks may contain "mixed ages," i.e., may have ages that are intermediate between the ages of end-member events. Two phenomena that may cause mixed ages are: (1) long-lasting reaction during the burial illitization of smectite: and (2) physical mixing of detrital and diagenetic components. The first phenomenon was investigated by simulation of illitization reactions using a nucleation and growth mechanism. These calculations indicate that values for mixed ages are related to burial history: for an equivalent length of reaction time, fast burial followed by slow burial produces much older mixed ages than slow burial followed by fast. The type of reaction that occurred in a rock can be determined from the distribution of ages with respect to the thickness of illite crystals. Dating of artificial mixtures confirms a non-linear relation between mixed ages and the proportions of the components. Vertical variation of K-Ar age dates from Gulf Coast shales can be modeled by assuming diagenetic illitization that overprints a subtle vertical trend (presumably of sedimentary origin) in detrital mineral content.

American Mineralogist↗

USGS2000

User's Guide to Galoper: A Program for Simulating the Shapes of Crystal Size Distributions from Growth Mechanisms - and Associated Programs

GALOPER is a computer program that simulates the shapes of crystal size distributions (CSDs) from crystal growth mechanisms. This manual describes how to use the program. The theory for the program's operation has been described previously (Eberl, Drits, and Srodon, 1998). CSDs that can be simulated using GALOPER include those that result from growth mechanisms operating in the open system, such as constant-rate nucleation and growth, nucleation with a decaying nucleation rate and growth, surface-controlled growth, supply-controlled growth, and constant-rate and random growth; and those that result from mechanisms operating in the closed system such as Ostwald ripening, random ripening, and crystal coalescence. In addition, CSDs for two types weathering reactions can be simulated. The operation of associated programs also is described, including two statistical programs used for comparing calculated with measured CSDs, a program used for calculating lognormal CSDs, and a program for arranging measured crystal sizes into size groupings (bins).

Open-File Report↗

USGS1998

Deducing growth mechanisms for minerals from the shapes of crystal size distributions

Crystal size distributions (CSDs) of natural and synthetic samples are observed to have several distinct and different shapes. We have simulated these CSDs using three simple equations: the Law of Proportionate Effect (LPE), a mass balance equation, and equations for Ostwald ripening. The following crystal growth mechanisms are simulated using these equations and their modifications: (1) continuous nucleation and growth in an open system, during which crystals nucleate at either a constant, decaying, or accelerating nucleation rate, and then grow according to the LPE; (2) surface-controlled growth in an open system, during which crystals grow with an essentially unlimited supply of nutrients according to the LPE; (3) supply-controlled growth in an open system, during which crystals grow with a specified, limited supply of nutrients according to the LPE; (4) supply- or surface-controlled Ostwald ripening in a closed system, during which the relative rate of crystal dissolution and growth is controlled by differences in specific surface area and by diffusion rate; and (5) supply-controlled random ripening in a closed system, during which the rate of crystal dissolution and growth is random with respect to specific surface area. Each of these mechanisms affects the shapes of CSDs. For example, mechanism (1) above with a constant nucleation rate yields asymptotically-shaped CSDs for which the variance of the natural logarithms of the crystal sizes (??2) increases exponentially with the mean of the natural logarithms of the sizes (??). Mechanism (2) yields lognormally-shaped CSDs, for which ??2 increases linearly with ??, whereas mechanisms (3) and (5) do not change the shapes of CSDs, with ??2 remaining constant with increasing ??. During supply-controlled Ostwald ripening (4), initial lognormally-shaped CSDs become more symmetric, with ??2 decreasing with increasing ??. Thus, crystal growth mechanisms often can be deduced by noting trends in ?? versus ??2 of CSDs for a series of related samples.

American Journal of Science↗

USGS1990

Ostwald ripening of clays and metamorphic minerals

Analyses of particle size distributions indicate that clay minerals and other diagenetic and metamorphic minerals commonly undergo recrystallization by Ostwald ripening. The shapes of their particle size distributions can yield the rate law for this process. One consequence of Ostwald ripening is that a record of the recrystallization process is preserved in the various particle sizes. Therefore, one can determine the detailed geologic history of clays and other recrystallized minerals by separating, from a single sample, the various particle sizes for independent chemical, structural, and isotopic analyses.

Science↗

USGS1988

Ostwald ripening and interparticle-diffraction effects for illite crystals

The Warren-Averbach method, an X-ray diffraction (XRD) method used to measure mean particle thickness and particle-thickness distribution, is used to restudy sericite from the Silverton caldera. Apparent particle-thickness distributions indicate that the clays may have undergone Ostwald ripening and that this process has modified the K-Ar ages of the samples. The mechanism of Ostwald ripening can account for many of the features found for the hydrothermal alteration of illite. Expandabilities measured by the XRD peak-position method for illite/smectites (I/S) from various locations are smaller than expandabilities measured by transmission electron microscopy (TEM) and by the Warren-Averbach (W-A) method. This disparity is interpreted as being related to the presence of nonswelling basal surfaces that form the ends of stacks of illite particles (short-stack effect), stacks that, according to the theory of interparticle diffraction, diffract as coherent X-ray scattering domains. -from Authors

American Mineralogist↗

USGS1987

Sericite from the Silverton caldera, Colorado: correlation among structure, composition, origin, and particle thickness.

The mineralogy and the origin of a suite of almost pure sericites, collected from fractures in hydrothermally altered volcanic rocks in the vicinity of the Silverton caldera in the western San Juan Mountains of Colorado, USA, are analysed.-J.A.Z.

American Mineralogist↗