Aquatic chemistry is becoming both a rewarding and substantial area of inquiry and is drawing many prominent scientists to its fold. Its literature has changed from a compilation of compositional tables to studies of the chemical reactions occurring within the aquatic environments. But more than this is the recognition that human society in part is determining the nature of aquatic systems. Since rivers deliver to the world ocean most of its dissolved and particulate components, the interactions of these two sets of waters determine the vitality of our coastal waters. This significant vol ume provides not only an introduction to the dynamics of aquatic chem istries but also identifies those materials that jeopardize the resources of both the marine and fluvial domains. Its very title provides its emphasis but clearly not its breadth in considering natural processes. The book will be of great value to those environmental scientists who are dedicated to keeping the resources of the hydrosphere renewable. As the size of the world population becomes larger in the near future and as the uses of materials and energy show parallel increases, the rivers and oceans must be considered as a resource to accept some of the wastes of society. The ability of these waters and the sediments below them to accommodate wastes must be assessed continually. The key questions relate to the capacities of aqueous systems to carry one or more pollutants."

Metal pollution in the aquatic environment

Dissimilatory Fe(III) and Mn(IV) reduction.

The composition of “heavy,” or accessory, detrital minerals in sediments and sedimentary rocks has been a topic of quantitative study for at least the last seventy years, beginning with the first issue of the Journal of Sedimentary Petrology in May 1931 (Tyler 1931, Pentland 1931). Zircon has since played a prominent and complex role in interpreting the composition and history of modern and ancient sediments. Because zircon is highly refractory at Earth’s surface, it occurs in virtually all sedimentary deposits and so provides a critical link in understanding the source history of a deposit. Twenhofel (1941), in a pioneering paper on the frontiers of sedimentary mineralogy and petrology, noted that the simple presence of detrital zircon would be of little value in determining its source: “Zircons from a half dozen sources with as many different properties may be present in a sediment and merely be identified as zircon. Parent rocks cannot be positively identified on such data . The variety or varieties must be identified and their optical properties determined.” From very early on, then, it was recognized that detrital zircon would be a powerful tool in understanding provenance, and thus, sedimentary dispersal systems.

Interpretive goals matured considerably in the subsequent decades, especially with major advances in microscopy, mineral chemistry, isotope tracer geochemistry, and geochronology, each addressing different aspects of provenance, sedimentation, and Earth history. The hundreds of published studies utilizing detrital zircon in the last 20 years indicate the increasing success in assessing provenance, paleogeography, and tectonic reconstructions. Selected studies are highlighted in this review to illustrate ways in which detrital zircon can be used for interpreting the stratigraphic record, and thus, the past surface conditions of Earth. In it we will outline the quantitative techniques involved in the sampling protocol and interpretation of data and then …

Detrital Zircon Analysis of the Sedimentary Record

A study of global sand seas

The Colorado River in its course from central Texas to the Gulf of Mexico carries quartz, chert, and limestone pebbles which can be traced for distances of up to 270 miles from their source. Limestone is so soft that it reaches its limiting roundness in the first few miles and thereafter undergoes no further increase. Harder quartz rounds much more slowly but eventually attains the same high limiting roundness value as limestone. Chert, being brittle, tends to spall and only rounds slightly downstream. A new and more behavioristic measure of equidimensionality, "maximum projection sphericity," is introduced, and a triangular diagram is proposed for analysis of the equant versus disklike versus rodlike aspect of particles, here termed "form." It was hoped that, by limiting the study to pebbles 32-64 mm. in length, the effects of grain size might be eliminated; the data show, however, that, even within this narrow range, particle size has a greater effect on sphericity and form than 200 miles of fluvial tra...

Pebbles in the Lower Colorado River, Texas a Study in Particle Morphogenesis

Clay minerals are classified and non-clay minerals in the clay fraction listed. Chapters follow on: the environment and occurence of clay minerals; various kinds, their structures and diffraction patterns; x-ray diffraction as applied to clay mineralogy; preparation of clays for x-ray examination; quantitative estimation of clay minerals in a mixture.

Clay minerals: A guide to their X-ray identification

Role of clay minerals in the transportation of iron

One-g samples of a montmorillonite, a metabentonite, an illite, two kaolinites, and three halloysites were treated with 50 ml of hydrochloric acid (6·45 N, 1: 1), acetic acid (4·5 N, 1: 3), sodium hydroxide (2·8N), sodium chloride solution (pH 6·10; Na = 35‰; Cl = 21·5‰), and natural sea water (pH 7·85; Na = 35·5‰; Cl = 21·5‰) for a 10-day period in stoppered plastic vials. The supernatant solutions were removed from the clay minerals and analyzed for SiO2, Al2O3, CaO, MgO, Na2O, and K2O. All the solutions removed some SiO2, Al2O3, and Fe2O3 from the samples, but the quantities were small. Sodium hydroxide attacked the kaolin group minerals more strongly than it did montmorillonite, metabentonite, or illite. Halloysite was more strongly attacked by hydrochloric acid than was any of the other experimental minerals. Hydrochloric acid removed iron oxide coatings from soil clay minerals, but acetic acid did not remove them completely. The samples most strongly attacked by HCl and NaOH were examined by X-ray diffraction. Acid treatment did not destroy the structure of the clays, but the halloysite structure was partially destroyed. Sodium hydroxide attacked the halloysite structure, as shown by chemical analysis and X-ray diffraction. These experiments show that treatment in dilute acids has no harmful effect in the preparation of clays for X-ray diffraction. Acetic acid is preferred to hydrochloric acid for this purpose. Hydrochloric acid cleans clay minerals by removing free iron oxide from the surface; acetic acid is less effective.

Reactivity of Clay Minerals With Acids and Alkalies

Samples of a montmorillonite, a mixed-layer mineral (mica and montmorillonite) “illite”, kaolinite, and halloysite were immersed in 50 ml sea-water for 10 days, and additional samples of the first three were immersed for 150 days. The exchangeable cations were determined both before and after treatment. It was found that Mg2+ ions from sea-water moved into the exchange positions in the minerals in preference to Ca2+ and Na+ ions. The H-form of these minerals showed a gradual adjustment to sea-water as measured by change in pH and filling of the exchange positions with cations other than H+. Kaolinite adjusted very rapidly, but montmorillonite and the mixed-layer mineral were slow. All the minerals reacted to yield appreciable amounts of SiO2, Al2O3, and Fe2O3 to the sea-water. The quantities yielded are in the order montmorillonite > mixed-layer mineral > “illite” > kaolinite > halloysite The solubility is considered to be due to direct solution of SiO2 in the sea-water and to removal of Al2O3 from the octahedral layer of the minerals. When H-clays were titrated with sea-water three distinct kinds of curves were obtained: (a) kaolinite; (b) mixed-layer mineral, “illite,” and halloysite; and (c) montmorillonite. The curves are similar to those obtained with clay minerals titrated with other alkaline solutions. Kaolinite reacts somewhat like a number of simple acids, but the curves for the other minerals are more complex and are related to the neutralization of H and its replacement in the exchange sites by metallic cations. The exchangeable cations were determined in the minerals after titration, and the results are similar to those obtained after immersing the minerals in sea-water. The volume of sea-water required to reach an end point at about pH 7.6 varies from 11 ml for kaolinite to 135 ml for montmorillonite and is related to the titratable alkalinity of the sea water and to the exchange capacity of the minerals.

Effect of Sea-Water on Clay Minerals1

Observations made on numerous grains of zircon from the heavy residues of soils from different areas indicate that zircon becomes corroded under certain conditions, particularly those of strong alkaline leaching associated with the development of a lateritic type of profile. Zircon crystals have a number of weak points, such as inclusions and zoning, which enable corrosion to set in; some of these are illustrated by photomicrographs. It is suggested, following information obtained from spring and ground-water chemical analyses, that Ca-bicarbonate and Na-bicarbonate rich waters may be able to dissolve zircon. Several experiments in the artificial weathering of zircon are described; one of these used a synthetic cation exchange resin. The results, obtained over a short period of time o ly, were negligible.

Dorothy Carroll

Papers

Clay minerals: A guide to their X-ray identification

Role of clay minerals in the transportation of iron

Reactivity of Clay Minerals With Acids and Alkalies

Effect of Sea-Water on Clay Minerals1

Weatherability of zircon