Engineering Geology, Second Edition
Illustrating key points with diagrams and photographs, this book introduces the techniques that engineers will need to learn about and understand the geological conditions in which they intend to build.
TABLE OF CONTENTS Engineering Geology, Second Edition
Chapter 1: Rock Types and Stratigraphy
According to their origin, rocks are divided into three groups, namely, the igneous, metamorphic and sedimentary rocks.
Igneous Rocks
Igneous rocks are formed when hot molten rock material called magma solidifies. Magmas are developed when melting occurs either within or beneath the Earth s crust, that is, in the upper mantle. They comprise hot solutions of several liquid phases, the most conspicuous of which is a complex silicate phase. Thus, igneous rocks are composed principally of silicate minerals. Furthermore, of the silicate minerals, six families the olivines [(Mg,Fe) 2SiO 4], the pyroxenes [e.g. augite, (Ca, Mg, Fe, Al) 2(Al,Si) 2O 6], the amphiboles [e.g. hornblende, (Ca,Na,Mg,Fe,Al) 7-8(Al,Si) 8O 22(OH) 2], the micas [e.g. muscovite, KAl 2(AlSi 2) 10(O,F) 2; and biotite, K(Mg,Fe) 2(AlSi 3)O 10(OH,F) 2], the feldspars (e.g. orthoclase, KAlSi 3O 8; albite, NaAlSi 3O 8; and anorthite, CaAl 2Si 2O 8) and the silica minerals (e.g. quartz, SiO 2) are quantitatively by far the most important constituents. Figure 1.1 shows the approximate distribution of these minerals in the commonest igneous rocks.
Figure 1.1: Approximate mineral compositions of the more common types of igneous rocks, e.g. granite approximately 40% orthoclase, 33% quartz, 13% plagioclase, 9% mica and 5% hornblende (plutonic types without brackets, volcanic equivalents in brackets).
Igneous rocks may be divided into intrusive and extrusive types, according to their mode of occurrence.
Copyright Elsevier Ltd. 2006 under license agreement with Books24x7
