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| | Geological Society - Teaching Resources - Rock Group Definitions |
 | | Sedimentary rocks are formed at the Earth's surface from the weathered and eroded fragments of pre-existing rocks (clastic sedimentary rocks, eg, quartz sandstone), from the hard parts of animals or plants (organic sedimentary rocks, eg, shelly limestone, coal), or from the precipitation out of solution of dissolved minerals (chemical sedimentary rocks, eg, rock salt, gypsum). |
 | | Metamorphic rocks are formed from the mineralogical and/or textural transformation, in the solid state, of pre-existing rocks due to the action of temperature and/or pressure. |
 | | Metamorphic rocks that have been subjected to deep burial typically display a foliated texture due to the parallel alignment of some constituent minerals (as in schist) or the segregation of minerals into separate bands of different composition (as in gneiss). |
| www.geolsoc.org.uk /template.cfm?name=rock_groups (218 words) |
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