Sedimentary rock

Sedimentary rocks are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentary rocks have also been found on Mars. Sedimentation is the collective name for processes that cause mineral and/or organic particles (detritus) to settle and accumulate or minerals to precipitate from a solution. Particles that form a sedimentary rock by accumulating are called sediment. Before being deposited, sediment was formed by weathering and erosion in a source area, and then transported to the place of deposition by water, wind, ice, mass movement or glaciers, which are called agents of denudation.

The sedimentary rock cover of the continents of the Earth's crust is extensive, but the total contribution of sedimentary rocks is estimated to be only 8% of the total volume of the crust. Sedimentary rocks are only a thin veneer over a crust consisting mainly of igneous and metamorphic rocks. Sedimentary rocks are deposited in layers as strata, forming a structure called bedding. The study of sedimentary rocks and rock strata provides information about the subsurface that is useful for civil engineering, for example in the construction of roads, houses, tunnels, canals or other structures. Sedimentary rocks are also important sources of natural resources like coal, fossil fuels, drinking water or ores.

Wikimedia Commons

Wikimedia Commons (or simply Commons) is an online repository of free-use images, sound, and other media files. It is a project of the Wikimedia Foundation.

Files from Wikimedia Commons can be used across all Wikimedia projects in all languages, including Wikipedia, Wikibooks, Wikivoyage, Wikispecies, Wikisource, and Wikinews, or downloaded for offsite use. The repository contains over 30 million media files. In July 2013, the number of edits on Commons reached 100,000,000.

History

The project was proposed by Erik Möller in March 2004 and launched on September 7, 2004. A key motivation behind the setup of a central repository was the desire to reduce duplication of effort across the Wikimedia projects and languages, as the same file had to be uploaded to many different wikis separately before Commons was created.

Several sister projects (e.g. Dutch, Swedish, Danish, Norwegian, Spanish, Basque, Polish, Czech and Slovak Wikipedias) moved all their media content to Commons and stopped allowing local uploading. Some projects, such as the English Wikipedia, have more compliant copyright policy and allow to upload and keep files which are not acceptable at Commons, e.g. fair use images.

Public domain

Works in the public domain are those whose exclusive intellectual property rights have expired, have been forfeited, or are inapplicable. For example, the works of Shakespeare and Beethoven, and most of the early silent films, are all now in the public domain by leaving the copyright term. Examples for works not covered by copyright which are therefore in the public domain, are the formulae of Newtonian physics, cooking recipes and all software before 1974. Examples for works actively dedicated into public domain by their authors are the Serpent encryption reference implementation,NIH's ImageJ, and the CIA's The World Factbook. The term is not normally applied to situations where the creator of a work retains residual rights, in which case use of the work is referred to as "under license" or "with permission".

As rights are country-based and vary, a work may be subject to rights in one country and be in the public domain in another. Some rights depend on registrations on a country-by-country basis, and the absence of registration in a particular country, if required, creates public domain status for a work in that country.

Rock (geology)

In geology, rock or stone 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.

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, which is an essential component of geology.

Classification

At a granular level, rocks are composed of grains of minerals, which, in turn, are homogeneous solids formed from a chemical compound that is arranged in an orderly manner. The aggregate minerals forming the rock are held together by chemical bonds. The types and abundance of minerals in a rock are determined by the manner in which the rock was formed. Many rocks contain silica (SiO₂); a compound of silicon and oxygen that forms 74.3% of the Earth's crust. This material forms crystals with other compounds in the rock. The proportion of silica in rocks and minerals is a major factor in determining their name and properties.