{"thcode":2,"term":{"code":883,"name":"petrology","parent":464,"scope":"Branch of earth sciences concerned with the origin, structure, alteration, and composition of rocks."},"uf":[],"bt":[{"code":464,"name":"geology","parent":291,"scope":"Study of the planet earth, its composition, structure, physical and chemical processes, and history since its origin."},{"code":291,"name":"earth sciences","parent":1019,"scope":"Broad term for all science related to the study of the earth."},{"code":1019,"name":"sciences","parent":1,"scope":"Major educational fields, fields of study, and professional groupings within USGS."},{"code":1,"name":"Categories","parent":null,"scope":"Thematic terms for categorizing information resources.  This thesaurus is intended to support finding and understanding scientific information."}],"nt":[],"rt":[{"code":248,"name":"diagenesis","parent":451,"scope":"Chemical, physical, and biological changes in sediment during and after its conversion to rock (lithification)."},{"code":572,"name":"igneous rocks","parent":1005,"scope":"Rocks formed from melted rock that has cooled and solidified."},{"code":725,"name":"metamorphic rocks","parent":1005,"scope":"Sedimentary or igneous rocks which have undergone such intense changes in temperature, pressure, structural stress, or chemical environment that they are transformed into denser rocks."},{"code":880,"name":"petrography","parent":619,"scope":"Use of optical microscopy for the description and classification of rocks."},{"code":1005,"name":"rocks and deposits","parent":287,"scope":"Solid masses that make up the earth's crust as well as accumulations of materials. Use for major rock types and unconsolidated deposits. For deposits of economic value, see related terms."},{"code":1035,"name":"sedimentary rocks","parent":1005,"scope":"Rocks formed by the consolidation of loose, uncemented pieces of sediments."}]}