GO 324 Rocks and Minerals Susan Ward Aber www.emporia.edu/earthsci/amber/go324/rock.htm

Emporia State University Emporia, Kansas USA Earth Science Department

Rocks are a natural aggregate of one or more minerals. The study of rocks draws upon mineralogy, geology, paleontology, chemistry, and physics. Ascertaining the textures, structures, mineral components, and organic remains when present are all key to identifying rocks. Mineral components and organic remains may be determined with the unaided eye, but often times positive identification will require high magnification or devices more sophisticated than a microscope. Texture refers to the size, shape, and arrangement of component constituents. Structure may describe the shape, dimensions and articulation of the component constituents (Simon & Schuster, 1978, p. 415). Textural and structural terms may vary with different rock classifications. Structures are usually visible on a geologic scale, whereas textures are on a hand specimen scale. Texture is the result of the formational environments and structures, the result of deformations.

There are three classifications of rocks found on Earth, igneous, sedimentary, and metamorphic. Earth is divided into a crust, mantle, and core, with the upper mantle and crust together referred to as the lithosphere. The lithosphere is divided into plates that are bounded by faults, subduction zones, and spreading centers. Even though the oceanic crust is primarily basalt and continental crust is primarily granite, the upper 10 miles of the lithosphere consists of 95% igneous or their metamorphic equivalents, 4% shale, 0.75% sandstone, and 0.25% limestone (Klein and Hurlbut, 1999, p. 221). Therefore, igneous and metamorphic rocks dominate the lithosphere volumetrically and sedimentary rock is primarily exposed as a thin covering over much of the Earth's continents. Raymond (1995) stated that a thin veneer of sedimentary rock covers 66% of the continental crust, while the remaining surficial exposures are equally divided between igneous and metamorphic (p. 3).