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1995 | Buch

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Origin and Mineralogy of Clays

Clays and the Environment

herausgegeben von: Dr. Bruce Velde

Verlag: Springer Berlin Heidelberg

Enthalten in: Professional Book Archive

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Origin and Mineralogy of Clays, the first of two volumes, lays the groundwork for a thorough study of clays in the environment. The second volume will deal with environmental interaction. Going from soils to sediments to diagenesis and hydrothermal alteration, the book covers the whole spectrum of clays. The chapters on surface environments are of great relevance in regard to environmental problems in soils, rivers and lake-ocean situations, showing the greatest interaction between living species and the chemicals in their habitat. The book is of interest to scientists and students working on environmental issues.

Inhaltsverzeichnis

Frontmatter

1. Geology of Clays

Abstract

The chapters which follow deal with the occurrence of clays in nature. This concerns the geology of clays: the geological processes which lead to the creation of clays, the transformation of clays and the destruction of clays in different geological environments. Clays, as is the case for most objects on the Earth, are ephemeral. They have a life span which is governed by their geologic history. Clays occur under a limited range of conditions in geological space [time and temperature (essentially depth)]. They are found mainly at the surface of the Earth: their origin is for the most part initiated in the weathering (rock-atmosphere interface) environment. Some clays form at the water-sediment interface (deep sea or lake bottom). A smaller number of clays form as a result of the interaction of aqueous solutions and rocks, either at some depth in the sedimentary pile or in the late stages of magmatic cooling (hydrothermal alteration). Although, this last occurrence is not of great extent it is very important to geologists as they have been called upon to aid human activity. Hydrothermal alteration often leads to the accumulation of useful heavy metals, such as gold, tungsten, and uranium. Therefore, when geologists encounter rocks which have altered to clay, and they determine that this occurred at depth (i.e. not weathering or superficial phenomena), they often take a sample in order to assess the heavy metal content. In addition to the accumulations of interesting metals, the extensive alteration of rocks due to hydrothermal alteration can produce pure clay deposits which are also of economic interest, e.g. clays for ceramics, and silica for industrial uses. Thus, as is often the case, the rare occurrence is of greater interest to humans than the more common, overall changes of geologic materials. However, in problems of environmental importance, the general, common occurrence is of greatest importance and the rare case is more of an anecdote. Environment is concerned with the everyday, while industry is concerned with the exceptions.

B. Velde

2. Composition and Mineralogy of Clay Minerals

Abstract

Clay minerals were initially defined on the basis of their crystal size. They were determined as the minerals whose particle diameters were less than 2 μm. This limit was imposed by the use of the petrographic microscope where the smallest particle which could be distinguished optically was of this size. Clays were essentially those minerals which could not be dealt with in a conventional nineteenth century manner. Chemical analyses were nevertheless made of fine grain size materials, most often with good results. However, the crystal structure and mineralogical family were only poorly understood. This was mainly due to the impurities present in clay aggregates, either as other phases or in multiphase assemblages. Slow progress was made in the early twentieth century, but the advent of reliable X-ray diffractometers allowed one to distinguish between the different mineral species found in the <2 μm grain size fraction. Today we know much more about clay mineral XRD (X-ray diffraction) properties; perhaps too much at times.

B. Velde

3. Origin of Clays by Rock Weathering and Soil Formation

Abstract

It is a fact that mankind’s domain of influence at the surface of the planet is roughly that of clay mineral formation: soils, weathered rocks, diagenetic series, continental and marine sediments, geothermal fields. These clay resources have been exploited since the discovery of fire. It is now important, for environmental studies, to know as well as possible, how and where these minerals form. Curiously, among the numerous works published until now, only a few are devoted to the mechanisms of clay formation at the scale of a soil profile, i.e. the metric scale in temperate zones. Indeed, more is known at the scale of a country (km) or the mineral-fluid interface (nm). For example, at the scale of a country, weathering can be considered as a homogeneous process. As a consequence, it is possible to model chemical transfers and clay-mineral stability fields using calculation codes. On the other extreme, the intimate dissolution-recrystallization mechanisms at the fluid-mineral interface scale are studied on isolated pure crystals in order to simplify the chemical system.

D. Righi, A. Meunier

4. Erosion, Sedimentation and Sedimentary Origin of Clays

Abstract

Of all the various types of sediment, fine-grained sediments with a high proportion of clay minerals are by far the most abundant. In the marine environment, terrigenous (land-derived) muds cover about 60% of the continental shelves, and almost 40% of the deep ocean basins, amounting in total to about a third of the Earth’s surface (Fig. 4.1). Similarly, although proportionally much smaller in area, continental aquatic environments are often dominated by fine-grained sediments, and these environments include many of the rivers, lakes, deltas and estuaries used extensively by man.

S. Hillier

5. Compaction and Diagenesis

Abstract

This chapter follows logically that dealing with the origins of clay in the sedimentation environment. Sedimentation followed by more sedimentation leads to diagenesis, burial diagenesis which is the most important diagenesis for silicates. What is the nature of the change in state which brings about new minerals upon their burial? As sediments accumulate in a basin (the basic concept of a sedimentary basin being a recipient that has a bottom which continues to grow deeper with time, a sort of un-filling cup; otherwise the recipient would fill up and the story would end) they are subjected to two major changes in their environment. First as burial proceeds, sediment temperature increases. As any miner knows, deep mines are hotter than shallow ones, and in fact the Earth is hotter inside than at its skin (i.e. the solid gas interface known as the Earth’s surface). So as sediments get buried in basins, or on the edges in continents, they get hotter.

B. Velde

6. Hydrothermal Alteration by Veins

Abstract

Sedimentary series, as well as crystalline basements, are cross-cut by fracture networks along which fluids of different origins (meteoric, connate, metamor-phic, magmatic) have percolated. Chemical interactions with rocks along these pathways produce secondary minerals among which phyllosilicates are usually the dominant species. The mineral deposit sealing the fracture and the altered wall rocks are described as hydrothermal veins. These veins have long been studied as guides for prospective ore deposits (Rose and Burt 1979). Pioneer studies have demonstrated that the altered wall rock is zoned, and that the zones develop simultaneously by outward growth of several alteration fronts (Sales and Meyer 1950). Compared to pervasive alteration systems (Chapter 7), the volume ratio of altered versus unaltered rock is several orders of magnitude lower in a vein system. Nevertheless, veins are of great importance in environmental problems because they concentrate clays in the zones of fluid circulation.

A. Meunier

7. Formation of Clay Minerals in Hydrothermal Environments

Abstract

Formation of clay minerals under hydrothermal influence is the result of rock alteration by circulating hot water in the Earth’s crust. A pre-existing rock-forming mineral assemblage is altered to a new set of minerals which are more stable under the hydrothermal conditions of temperature, pressure, and fluid composition. The interaction of hot water and rocks forms a spatially and temporally regular zonal pattern of new clay minerals, as the fluid with cooling temperature moves through the surrounding rock mass. This chapter discusses the formation of clay minerals in such dynamic processes of hydrothermal alteration. The approach is one of clay-mineral facies formed under conditions of massive alteration in the rocks. The chemical and mineralogical changes which occur on the scale of a rock or rock mass are considered to have been dealt with in the preceding chapter. The exact process of change via local, vein-influenced exchange processes is ignored for simplicity (see Chap. 6).

A. Inoue

Backmatter

Titel: Origin and Mineralogy of Clays
herausgegeben von: Dr. Bruce Velde
Verlag: Springer Berlin Heidelberg
Electronic ISBN: 978-3-662-12648-6
Print ISBN: 978-3-642-08195-8
DOI: https://doi.org/10.1007/978-3-662-12648-6

Springer Professional

Über dieses Buch

Inhaltsverzeichnis

Frontmatter

1. Geology of Clays

2. Composition and Mineralogy of Clay Minerals

3. Origin of Clays by Rock Weathering and Soil Formation

4. Erosion, Sedimentation and Sedimentary Origin of Clays

5. Compaction and Diagenesis

6. Hydrothermal Alteration by Veins

7. Formation of Clay Minerals in Hydrothermal Environments

Backmatter