Rocks and Meteorites

Abstract

Rocks represent the overall geological materials constituting the Earth’s crust (lithosphere), which are commonly made from an aggregate of crystals of one or more minerals and/or glass. From a wide geological point of view, rocks can be either solid (e.g., granite, limestone, rock salt, and ice), or fluid (e.g. sand and volcanic ashes), or liquid (bitumen and oil), or gaseous (natural gas and hydrothermal fluids). The important discipline of Earth sciences which studies the rock formation processes, chemical composition and physical properties, is named petrology (from Latin, petrus, stone) sometimes called lithology in the old textbooks (from Greek, lithos, stone), while petrography sensu-stricto only classifies rocks and can be understood as simple taxonomy. There are several reasons to study, identify, and measure properties of the different types of rocks present in the Earth’s crust. First of all, rock materials contain valuable mineral ore deposits and can also contain fossil fuels (e.g., oil, coal, and natural gas). Hence understanding of the different types of rocks is necessary in order to locate and recover these valuable economical resources. Secondly, from a civil engineering point of view, the knowledge of the physical properties of different rocks used in construction is important to select the most appropriate building materials. Actually, some rock types are more susceptible to slope failure (landslides) or structural failure (disintegration under pressure) than others. Consequently, it is necessary to know the characteristics of the underlying rocks when doing any major civil engineering construction. Thirdly, from an agricultural point of view, rocks are the basic geological material from which all soils are formed. Hence, the rock chemical composition strongly influences the nature of the soil and the types of vegetation which the soil can support. Finally, from an environmental point of view, rock type also influences the flow of water, a major necessity of life, above and below the ground surface.