<descriptor thcode="2"><thesaurus thcode="2" name="USGS Thesaurus" scope="Topics and methods of scientific study carried out by USGS, with product types, scientific disciplines, geologic time, and types of institutional structure and activities.  Broad and shallow, used to help people find scientific information." creator="U.S. Geological Survey" rights="Public domain" edition="2.0" date="2020-01-09" codetype="number" prefix="topic" uri="https://www2.usgs.gov/science/USGSThesaurus" tblname="term" nonpref="nonpref" relterm="relterm" root_code="1" contact="pschweitzer"><category><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/></category><altlabel><altlabel>USGSThesaurus</altlabel><altlabel>USGSThesaurus</altlabel></altlabel></thesaurus><term thcode="2" code="312" name="economic geology" parent="464" scope="Scientific study of the formation, location, and use of marketable geologic materials including fuels, metals, minerals, and water."/><bt><term thcode="2" code="464" name="geology" parent="291" scope="Study of the planet earth, its composition, structure, physical and chemical processes, and history since its origin."/><term thcode="2" code="291" name="earth sciences" parent="1019" scope="Broad term for all science related to the study of the earth."/><term thcode="2" code="1019" name="sciences" parent="1" scope="Major educational fields, fields of study, and professional groupings within USGS."/><term thcode="2" code="1" name="Categories" scope="Thematic terms for categorizing information resources.  This thesaurus is intended to support finding and understanding scientific information."/></bt><rt><term thcode="2" code="132" name="building stone resources" parent="798" scope="Deposits of rocks used in construction, including crushed stone and dimension stone. Dimension stone includes limestone and granite, quarried in large blocks, and shaped in cubes, panels and other forms."/><term thcode="2" code="164" name="clay deposits" parent="1199" scope="Fine-grained sedimentary soil deposits, containing hydrated silicas of aluminum, that are plastic and sticky when wet and harden when heated."/><term thcode="2" code="172" name="coal resources" parent="799" scope="Fuel resources such as anthracite, lignite, bituminous coal, or coke, consisting largely of carbonaceous material and formed from fossilized plants."/><term thcode="2" code="173" name="coalbed methane resources" parent="770" scope="Resources of methane-rich gas generated and stored in coalbeds."/><term thcode="2" code="799" name="energy resources" parent="777" scope="Natural resources that are used for heat and power generation, including oil, natural gas, coal, and geothermal energy."/><term thcode="2" code="427" name="gas hydrate resources" parent="770" scope="Deposits of a crystalline solid in which water molecules trap gas molecules, usually methane, in a cagelike structure known as a clathrate occurring in sediments overlain by cold deep water."/><term thcode="2" code="429" name="gem resources" parent="798" scope="Deposits of rare minerals prized for their color, durability, sparkle, and clarity when cut and polished and used as ornaments or jewelry."/><term thcode="2" code="500" name="gravel deposits" parent="1199" scope="Alluvial accumulations of small unconsolidated rock fragments, such as pebbles and cobbles, used in construction as fill, ground cover, or aggregate for concrete."/><term thcode="2" code="2295" name="hydrocarbon reservoir processes" parent="101" scope="Interactions among groundwater, hydrocarbons, and rock properties of subsurface geological formations, affecting the potential of those formations to form, trap, and permit the passage and extraction of hydrocarbons."/><term thcode="2" code="724" name="metallic mineral resources" parent="745" scope="Resources from which ductile, malleable, opaque,and reflective metals that are also good heat and electricity conductors can be extracted."/><term thcode="2" code="745" name="mineral resources" parent="777" scope="Natural occurrences of useful inorganic elements or compounds."/><term thcode="2" code="770" name="natural gas resources" parent="799" scope="Stocks of naturally formed hydrocarbon gases which are usually associated with petroleum fields.  Useful for heating, they are principally methane, but can be ethane, butane, or propane."/><term thcode="2" code="798" name="nonmetallic mineral resources" parent="745" scope="Useful mineral deposits that are not metals.  Includes materials used for construction, decoration, fuel, and industrial purposes."/><term thcode="2" code="829" name="oil resources" parent="799" scope="Deposits (pools) of highly valuable liquid hydrocarbons or fossil fuels."/><term thcode="2" code="830" name="oil sand resources" parent="829" scope="Deposits of sandstone or unconsolidated sand containing bitumen that can be extracted as an oil resource."/><term thcode="2" code="831" name="oil shale resources" parent="829" scope="Deposits of finely grained sedimentary rock containing kerogen that can be distilled to produce liquid or gaseous hydrocarbons."/><term thcode="2" code="1011" name="sand deposits" parent="1199" scope="Deposits of loose particles of rock or mineral (sediment) that range in size from 0.0625-2.0 millimeters in diameter."/><term thcode="2" code="1080" name="soil resources" parent="777" scope="Natural resources of unconsolidated fragmented rock, humus, and mineral matter that cover the surface of the earth."/></rt></descriptor>