{"thcode":4,"term":{"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."},"uf":[],"bt":[{"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."},{"code":"0","name":"Earth material","parent":null,"scope":"Geologic map unit classification (Bruce R. Johnson) version 6.2: A hierarchical classification of earth materials for digital geologic maps."}],"nt":[{"code":"3.1.1","name":"Obsidian","parent":"3.1","scope":"A black or dark-colored volcanic glass, usually of rhyolite composition, characterized by conchoidal fracture."},{"code":"3.1.3","name":"Pumice","parent":"3.1","scope":"A light-colored vesicular glassy rock commonly having the composition of rhyolite."},{"code":"3.1.2","name":"Vitrophyre","parent":"3.1","scope":"Any porphyritic igneous rock having a glassy groundmass."}],"rt":[]}