<descriptor thcode="4"><thesaurus thcode="4" name="Lithologic classification of geologic map units" scope="Rock types commonly found on geologic maps. Terms may combine compositional, textural, and genetic characteristics. Also includes unconsolidated materials that may be mapped as units. Not specific enough for categorizing hand samples or outcrops." creator="U.S. Geological Survey" rights="Public domain" edition="6.2" date="2004-08-16" codetype="alpha" prefix="lithclass" uri="http://www.usgs.gov/science/Lithclass6.2" tblname="lith" nonpref="lithnp" relterm="lithrt" root_code="0" contact="pschweitzer"><category><term thcode="25" code="10" name="persons" parent="2" scope="Terms specify individual people, typically by name."/><term thcode="25" code="30" name="ambiguous labels" parent="26" scope="A given preferred label may be used for more than one concept in the thesaurus. A concept must be specified using its unique identifier (code). This may occur in the names of places or people."/><term thcode="25" code="17" name="pseudohierarchical" parent="11" scope="Broader-narrower relationships exist in the vocabulary but have no semantic relation to the terms themselves, for example, a list of peoples' names arranged hierarchically by the first letter of the surname."/><term thcode="25" code="14" name="not transitive" parent="12" scope="Narrower terms cannot reliably be understood as parts of, types of, or instances of the terms that are broader than them."/><term thcode="25" code="9" name="organizations" parent="2" scope="Terms specify human organizations, their subdivisions and relationships, as well as characteristics of such organizations."/><term thcode="25" code="10" name="persons" parent="2" scope="Terms specify individual people, typically by name."/><term thcode="25" code="30" name="ambiguous labels" parent="26" scope="A given preferred label may be used for more than one concept in the thesaurus. A concept must be specified using its unique identifier (code). This may occur in the names of places or people."/><term thcode="25" code="17" name="pseudohierarchical" parent="11" scope="Broader-narrower relationships exist in the vocabulary but have no semantic relation to the terms themselves, for example, a list of peoples' names arranged hierarchically by the first letter of the surname."/><term thcode="25" code="14" name="not transitive" parent="12" scope="Narrower terms cannot reliably be understood as parts of, types of, or instances of the terms that are broader than them."/><term thcode="25" code="9" name="organizations" parent="2" scope="Terms specify human organizations, their subdivisions and relationships, as well as characteristics of such organizations."/></category><altlabel><altlabel>Lithclass6.2</altlabel><altlabel>Lithclass6.2</altlabel></altlabel></thesaurus><term thcode="4" code="5" name="Metamorphic rock" parent="0" scope="A rock derived from pre-existing rocks by mineralogical, chemical, and/or structural changes, essentially in the solid state, in response to marked changes in temperature, pressure, shearing stress, and chemical environment, generally at depth in the earth's crust."/><bt><term thcode="4" code="0" name="Earth material" scope="Geologic map unit classification (Bruce R. Johnson) version 6.2: A hierarchical classification of earth materials for digital geologic maps."/></bt><nt><term thcode="4" code="5.8" name="Amphibolite" parent="5" scope="A crystalloblastic rock consisting mainly of amphibole and plagioclase with little or no quartz."/><term thcode="4" code="5.13" name="Calc-silicate rock" parent="5" scope="A metamorphic rock consisting mainly of calcium-bearing silicates such as diopside and wollastonite, and formed by metamorphism of impure limestone or dolomite."/><term thcode="4" code="5.10" name="Eclogite" parent="5" scope="A granular rock composed essentially of garnet (almandine-pyrope) and sodic pyroxene (omphacite)."/><term thcode="4" code="5.7" name="Gneiss" parent="5" scope="A foliated rock formed by regional metamorphism, in which bands or lenticles of granular minerals alternate with bands or lenticles in which minerals having flaky or elongate prismatic habits predominate. Generally less than 50% of the minerals show preferred orientation."/><term thcode="4" code="5.6" name="Granofels" parent="5" scope="A medium- to coarse-grained granoblastic metamorphic rock with little or no foliation or lineation."/><term thcode="4" code="5.9" name="Granulite" parent="5" scope="A metamorphic rock consisting of even-sized, interlocking mineral grains less than 10% of which have any obvious preferred orientation."/><term thcode="4" code="5.11" name="Greisen" parent="5" scope="A pneumatolytically altered granitic rock composed largely of quartz, mica, and topaz."/><term thcode="4" code="5.1" name="Hornfels" parent="5" scope="A fine-grained rock composed of a mosaic of equidimensional grains without preferred orientation and typically formed by contact metamorphism."/><term thcode="4" code="5.2" name="Metasedimentary rock" parent="5" scope="A sedimentary rock that shows evidence of having been subjected to metamorphism."/><term thcode="4" code="5.3" name="Metavolcanic rock" parent="5" scope="A volcanic rock that shows evidence of having been subjected to metamorphism."/><term thcode="4" code="5.4" name="Phyllite" parent="5" scope="A metamorphosed rock, intermediate in grade between slate and mica schist. Minute crystals of graphite, sericite, or chlorite impart a silky sheen to the surfaces of cleavage (or schistosity)."/><term thcode="4" code="5.5" name="Schist" parent="5" scope="A strongly foliated crystalline rock, formed by dynamic metamorphism, that can be readily split into thin flakes or slabs due to the well developed parallelism of more than 50% of the minerals present, particularly those of the lamellar or elongate prismatic habit, e.g. mica and hornblende."/><term thcode="4" code="5.14" name="Serpentinite" parent="5" scope="A rock consisting almost wholly of serpentine-group minerals derived from the hydration of ferromagnesian silicate minerals such as olivine and pyroxene."/><term thcode="4" code="5.12" name="Skarn" parent="5" scope="A rock of complex mineralogic composition formed by contact metamorphism and metasomatism of carbonate rocks.  It is typically coarse-grained and rich in garnet, iron-rich pyroxene, epidote, wollastonite, and scapolite."/></nt></descriptor>