Texture (geology)

In geology, texture or rock microstructure[1] refers to the relationship between the materials of which a rock is composed.[2] The broadest textural classes are crystalline (in which the components are intergrown and interlocking crystals), fragmental (in which there is an accumulation of fragments by some physical process), aphanitic (in which crystals are not visible to the unaided eye), and glassy (in which the particles are too small to be seen and amorphously arranged).[2] The geometric aspects and relations amongst the component particles or crystals are referred to as the crystallographic texture or preferred orientation. Textures can be quantified in many ways.[3] A common parameter is the crystal size distribution. This creates the physical appearance or character of a rock, such as grain size, shape, arrangement, and other properties, at both the visible and microscopic scale.

Textures are penetrative fabrics of rocks; they occur throughout the entirety of the rock mass on microscopic, hand-sized specimen, and often outcrop scales. This is similar in many ways to foliations, except a texture does not necessarily carry structural information in terms of deformation events and orientation information. Structures occur on a hand-sized specimen scale and above.

Microstructure analysis [4] describes the textural features of the rock, and can provide information on the conditions of formation, petrogenesis, and subsequent deformation, folding, or alteration events.[5]

Crystalline textures include phaneritic, foliated, and porphyritic.[2] Phaneritic textures are where interlocking crystals of igneous rock are visible to the unaided eye. Foliated texture is where metamorphic rock is made of layers of materials.[2] Porphyritic texture is one in which larger pieces (phenocrysts) are embedded in a background mass made of much finer grains.[2]

Fragmental textures include clastic, bioclastic, and pyroclastic.[2]

A preferred mineral orientation, is the texture of metamorphic rock in which its grains have a flattened shape (inequant), and their planes tend to be oriented in the same direction.[6]

Texture in a thin section of mylonitic quartzite from the Alps, Italy
Texture in a thin section of tholeiitic basalt
  1. ^ Vernon, R. H. (2004). A practical guide to rock microstructure. Cambridge University Press. ISBN 0-521-81443-X.
  2. ^ a b c d e f Texture & Genesis of Rocks, Introductory Geology Laboratory, Christopher DiLeonardo, Ph.D., Marek Cichanski, Ph.D., Earth & Space Sciences, De Anza College
  3. ^ Higgins, M. D. (2006). Quantitative Textural Measurements in Igneous and Metamorphic Petrology. Cambridge: Cambridge University Press. ISBN 0-521-13515-X.
  4. ^ Fu, Jinlong; Thomas, Hywel R.; Li, Chenfeng (January 2021). "Tortuosity of porous media: Image analysis and physical simulation" (PDF). Earth-Science Reviews. 212: 103439. Bibcode:2021ESRv..21203439F. doi:10.1016/j.earscirev.2020.103439. S2CID 229386129.
  5. ^ Voznesensky, A. S.; Kidima-Mbombi, L. K. (2021-07-14). "Formation of synthetic structures and textures of rocks when simulating in COMSOL Multiphysics". Gornye Nauki I Tekhnologii = Mining Science and Technology (Russia). 6 (2): 65–72. doi:10.17073/2500-0632-2021-2-65-72. ISSN 2500-0632. S2CID 237797248.
  6. ^ Essentials of Geology, 3rd Ed, Stephen Marshak