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pyroclastic flow
(Encyclopedia)pyroclastic flow, turbulent, fluidized mixture of rock, volcanic ash, and hot gas that moves like an avalanche away from a volcanic eruption. A pyroclastic flow may contain a mix of rock fragments ran...taconite
(Encyclopedia)taconite, low-grade iron ore, a flintlike rock usually containing less than 30% iron. Resistant to drilling and to the extraction of its contained metal, the rock was long considered worthless. Experi...Garden of the Gods
(Encyclopedia)Garden of the Gods, park, 770 acres (312 hectares), central Colo., near Colorado Springs; noted for its unusual, multicolored rock formations. Narrow-crested sandstone hills and ridges have been erode...porphyry, igneous rock
(Encyclopedia)porphyry pôrˈfərē [key], igneous rock composed of large, conspicuous crystals (phenocrysts) and a groundmass in which the phenocrysts are embedded. Some authorities consider the expression “porp...music video
(Encyclopedia)music video, videotaped performance of a recorded popular song, usually accompanied by dance or a fragmentary story and sometimes employing concert footage. Typically three to five minutes long, music...slate
(Encyclopedia)slate, fine-grained rock formed when sedimentary rocks such as shale are metamorphosed by great pressure. Slate splits into perfectly cleaved, broad thin layers; this characteristically regular and pl...conglomerate, in geology
(Encyclopedia)conglomerate, in geology, sedimentary rock composed largely of pebbles or other rounded particles whose diameter is larger than 2 mm (.08 in.). Essentially a cemented gravel, conglomerates are formed ...boulder, in geology
(Encyclopedia)boulder, large rock fragment formed by detachment from its parent consolidated rock by weathering and erosion. In engineering and geology, especially in the United States, the term is applied to loose...batholith
(Encyclopedia)batholith, enormous mass of intrusive igneous rock, that is, rock made of once-molten material that has solidified below the earth's surface (see rock). Batholiths usually are granitic (see granite) i...mesa, in geology
(Encyclopedia)mesa māˈsə [key] [Span.,=table], name given in the SW United States to a small, isolated tableland or a flat-topped hill. Two or more of the sides are steep and usually perpendicular and some have ...Browse by Subject
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