Petrology
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This document provides an overview of petrology, the scientific study of rocks. It defines different types of rocks, including igneous rocks formed by cooling magma, sedimentary rocks formed from compacted sediments, and metamorphic rocks formed by changes to existing rocks through heat, pressure, and chemical processes. It describes key concepts such as crystallization, dykes and sills which are rock intrusions, and the textures and structures of different rock types that provide clues to their formation histories. The document emphasizes that rocks have been essential to human civilization and the development of tools and materials throughout history.
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Petrology
- 1. PETROLOGY K. TARUN KUMAR STRUCTURAL ENGINEERING
- 2. Definition of rock: • In geology, rock is a naturally occurring solid aggregate of one or more minerals or mineraloids. • For example, the common rock granite is a combination of the quartz, feldspar and biotite minerals. The Earth's outer solid layer, the lithosphere, is made of rock.
- 3. • Rocks have been used by mankind throughout history. From the Stone Age, rocks have been used for tools. The minerals and metals found in rocks have been essential to human civilization. • Three major groups of rocks are defined: Igneous, Sedimentary, and Metamorphic. The scientific study of rocks is called petrology.
- 5. Dykes and sills: • Dyke” and “sill” are geological terms used to describe an intrusion, usually a mass of igneous or volcanic rocks that forcibly entered, penetrated, and embedded into layers of another rock or land form. Dykes and sills are often associated with volcanoes though they are not exclusive to that particular land form.
- 6. • Dikes can be either intrusive or sedimentary in origin. • For example, when molten rock intrudes into a crack then crystallizes, it is an igneous dike. When sediment fills a pre- existing crack, it is aclastic dike.
- 8. • A dike or dyke in geological usage is a sheet of rock that formed in a fracture in a pre-existing rock body. • However, when the new rock forms within and parallel to the bedding of a layers rock, it is called a sill. • It is a type of tabular or sheet intrusion, that either cuts across layers in a planar wall rock structures, or into a layer or unlayered mass of rock.
- 9. Structure and texture of igneous rocks: • The texture of igneous rocks depends on the compositio n of the magma and the conditions surrounding the magma’s cooling. • The textures are different in intrusive, vein, and extrusiv e rocks. Intrusive rocks are characterized by aholocrystalline texture, in which all the rock material is crystallized. • Also depends on the shape of the crystals of the compone nt minerals.
- 10. Structure and texture of Sedimenatry rocks: • The relationship between rock structure and texture and rock genesis is more pronounced insedimentary rocks than in igneous rocks. • Clastic rocks consist of detrital (clastic) grains of various sizes and shapes. • The grains, which canbe angular, subrounded, or rounded, sometim es lie freely without attachment. • The structure of clastic rock, which depends on the mutual arrangem ent of the grains, can be random, laminar, or fluidal. With a random structure, the particles do not have an ordered arrangement.
- 11. Texture and structure of metamorphic rocks: • The structures and textures of metamorphic rocks arise d uring the recrystallization in thesolid state of primary sedi mentary and magmatic rocks. • The recrystallization occurs under the action of lithostatic pressure, temperature. • Which leads to an ordered arrangement of the mineral Grains.
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