<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="3" name="Volcanic rock" parent="0" scope="A generally finely crystalline or glassy igneous rock resulting from volcanic action at or near the Earth's surface, either ejected explosively or extruded as a lava.  The term includes near-surface intrusions that form a part of the volcanic structure."/><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="3.7" name="Alkalic volcanic rock" parent="3" scope="A volcanic rock that contains more sodium and/or potassium than is required to form feldspar with the available silica."/><term thcode="4" code="3.4" name="Felsic volcanic rock" parent="3" scope="A light-colored, fine-grained or aphanitic extrusive or hypabyssal rock, with or without phenocrysts and composed chiefly of quartz and feldspar."/><term thcode="4" code="3.1" name="Glassy volcanic rock" parent="3" scope="Extrusive rock having a texture which is similar to that of glass or quartz and developed as a result of rapid cooling of the lava without distinct crystallization."/><term thcode="4" code="3.5" name="Intermediate volcanic rock" parent="3" scope="A solidified body of volcanic rock having approximately equal light- and dark-colored minerals in its mode"/><term thcode="4" code="3.3" name="Lava flow" parent="3" scope="A solidified body of rock that is formed by the lateral, surficial outpouring of molten lava from a vent or a fissure."/><term thcode="4" code="3.6" name="Mafic volcanic rock" parent="3" scope="A solidified body of volcanic rock having abundant dark-colored minerals in its mode "/><term thcode="4" code="3.2" name="Pyroclastic rock" parent="3" scope="...clastic rock material formed by volcanic explosion or aerial expulsion from a volcanic vent."/><term thcode="4" code="3.8" name="Ultramafitite" parent="3" scope="A volcanic rock with color index (M) greater than or equal to 90"/><term thcode="4" code="3.9" name="Volcanic carbonatite" parent="3" scope="A rock of apparent volcanic origin composed of at least 50% carbonate minerals"/></nt></descriptor>