Details Title: Chapter 4 - Volcanism and Extrusive Rocks Description: midterm number 1 Total Flash Cards: 29 Created: 09/20/2009 08:07:39		New Users: To study from this flashcard set, or to create your own your own study flash cards, REGISTER HERE. Existing Users: CLICK HERE. Additional Geology Flashcards
Cards in this set: Term pyroclasts Definition rock fragments Term lava Definition magma on earth's surface Term extrusive rock Definition surface rock resulting form volcanic activity Term silicic or felsic rocks Definition silica rich  65% or more Term mafic rocks Definition silica deficient rocks 50% Term intermediate rocks Definition chemical content between that of silicic and mafic. Term pyroclastic flow Definition a mixture of gas and pyroclastic debris that is so dense that it hugs the ground as it flows rapidly into low areas. Term rhyolite Definition a silicic rock usually cream colored, tan or pink made up of mostly feldspar but always includes some quartz Term andesite Definition crystallizes from an intermediate lava moderately gray or green color Term basalt Definition has a relatively low amount of silica (50%) Term texture Definition refers to a rock's appearance with respect to the size, shape, and arrangement of its grains or other constituents.  Term fine grained rock Definition one in which most of the mineral grains are smaller than 1 millimeter. Term obsidian Definition volcanic glass one of the few rocks that is not composed of minerals. fine grained or glassy texture distinguishes extrusive rocks from most intrusive rocks. Term porphyritic Definition one in which larger crystals are enclosed in a groundmass of much finer grained minerals or obsidian. the larger crystals are termed phenocrysts. Term vesicles Definition cavities in extrusive rock resulting form gas bubbles that were in lava, and the texture is called vesicular. Term pumice Definition a frothy glass with so much void space that it floates in water. Term blocks Definition solid rock has been blasted apart by volcanic explosion pyroclastic fragments are angular, not rounded Term bomb Definition spindle or lens shaped pyroclast occurs when lava is ejected into the air. Term tuff Definition rock composed of fine grained pyroclastic particles Term volcanic breccia Definition a rock that includes larger pieces of volcanic rock Term vent Definition opening through which eruption takes place Term flank eruption Definition lava pours from a vent on the side of a volcano Term caldera Definition volcanic depression much larger than the original crater Term shield volcanoes Definition broad, gently sloping volcanoes constructed of solidified lava flows. Term cinder cone Definition a volcano constructed of pyroclastic fragments ejected from a central vent Term composite volcano Definition one constructed of alternating layers of pyroclastic fragments and solidified lava flows. Term volcanic domes Definition steep sided or spine shaped masses of volcanic rock formed from  viscous lava that solidifies in or immediately  above a volcanic vent Term columnar structure or jointing Definition individual layers may appear to be formed of parallel, vertical columns, mostly six-sided. Term pillow structure Definition rocks, gernerally basalt, occuring as pillow shapped, rounded masses closely fitted together.