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Minerals, rocks, discontinuities and rock mass
Published in Ömer Aydan, Rock Mechanics and Rock Engineering, 2019
Igneous rocks are created by melting and crystallization of magma. When the magma reaches the surface, the rocks are said to be extrusive (Fig. 2.4). Volcanic lava flows are examples of extrusive igneous rocks. If the magma cools within the Earth, it forms large bodies of crystalline rock called plutons or batholiths. These rocks are called intrusive igneous rocks. Igneous rocks are generally classified on the basis of three factors: (1) grain size and texture, (2) intrusive or extrusive, (3) silica content and mineral composition (Fig. 2.5). However, the classifications based on factors 2 and 3 are commonly used to describe igneous rocks as described next.
Minerals and rocks
Published in A.C. McLean, C. D. Gribble, Geology for Civil Engineers, 2017
Extrusive igneous rocks have formed (as lavas) by rapid cooling of magma at the surface, and are fine grained. Conversely, most, but not all, fine-grained igneous rocks are extrusive. Hypabyssal igneous rocksform minor intrusions (dykes and sills, see Section 2.2.3) which have solidified below the surface, and have cooled more slowly than extrusive rocks because of the thermal insulation of the surrounding country rocks. They are typically, but not invariably, medium grained. Plutonic igneous rocks have formed by the slow cooling of great volumes of magma, typically at depths of a few kilometres, within the Earth. It is erosion throughout geological time that has removed the overlying rocks and revealed these plutonic intrusions at the surface. The heat from their enormous bulk can dissipate only very slowly and they are normally coarse grained.
Rock drilling methods
Published in Lopez Jimeno Carlos, Lopez Jimeno Emilio, Javier Ayala Carcedo Francisco, Ramiro Yvonne Visser de, Drilling and Blasting of Rocks, 2017
Lopez Jimeno Carlos, Lopez Jimeno Emilio, Javier Ayala Carcedo Francisco, Ramiro Yvonne Visser de
Igneous rocks are formed by solidification from a molten mass, called magma, which is a mixture of dissolved rock and gas material. If the rock has cooled in contact with air or water from the earth’s surface it is classified as extrusive or volcanic igneous rock. When the magma cools underneath the surface of the earth it forms intrusive or plutonic igneous rock.
Formation of Cu–Au porphyry deposits: hydraulic quartz veins, magmatic processes and constraints from chlorine
Published in Australian Journal of Earth Sciences, 2023
G. N. Phillips, J. R. Vearncombe, J. D. Clemens, A. Day, A. F. M. Kisters, B. P. Von der Heyden
Magma is molten rock material that originates beneath the Earth’s surface and may be emplaced and cooled to become an igneous rock. We use the term magma to encompass the molten rock, the dissolved volatiles (gases) and the minerals crystallised from the melt or picked up from elsewhere in the crust. Magmas typically include enclaves of incorporated rocks and smaller aggregates of mineral grains. For porphyry deposits, this discussion of magma is confined to partially molten systems dominated by silicate melt components. Not all previous studies have used the term magma consistently and, to avoid uncertainty, we commonly discuss the separate components of magmas, as listed above.