reddish, due to presence of iron oxides, or greenish, due to presence of glauconite.Sanidine - A form of potash feldspar identical in composition with orthoclase but physically different, formed under different conditions and occurring in different rock types. It is the high temperature form of orthoclase, into which it inverts at 900C. Occurs in lavas and dyke rocks.Schist - group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. In the French, schist must be understood as shale.Sediment trap - a depression where sediments substantially accumulate over time.Sequence (geology) - a sequence of geological events, processes, or rocks, arranged in chronological order.Sericite - A white potash-mica, like muscovite in chemical composition and general character but occurring as a secondary mineral, often as a decomposition product of orthoclase.Shale - a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments (silt-sized particles) of other minerals, especially quartz and calcite.Shear zone - a tabular to sheetlike, planar or curviplanar zone composed of rocks that are more highly strained than rocks adjacent to the zone. See also Fault.Shield - a large area of exposed Precambrian crystalline igneous and high-grade metamorphic rocks that form tectonically stable areasSilcrete - an indurated soil duricrust formed when surface sand and gravel are cemented by dissolved silica.Silt - granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment (also known as suspended load) in a surface water body. It may also exist as soil deposited at the bottom of a water body.Slate - very fine-grained sedimentary rock of the clay or silt grade which as a consequence of regional metamorphism has developed a slaty cleavage.Slaty cleavage - The property of splitting easily along regular, closely spaced planes of fissility, produced by pressure in fine grained rocks, the cleavage planes lying in the directions of maximum elongation of the mass.Slickenside - a smoothly polished surface caused by frictional movement between rocks along the two sides of a fault. This surface is normally striated in the direction of movement.Slump - a form of mass wasting that occurs when a coherent mass of loosely consolidated materials or rock layers moves a short distance down a slope.Soil liquefaction - process describing the behavior of soils that, when loaded, suddenly suffer a transition from a solid state to a liquefied state, or having the consistency of a heavy liquid.Sorting - Sorting describes the distribution of grain size of sediments, either in unconsolidated deposits or in sedimentary rocks. Very poorly sorted indicates that the sediment sizes are mixed (large variance); whereas well sorted indicates that the sediment sizes are similar (low variance).Sphene - Titanite, or sphene, is a calcium titanium nesosilicate mineral.Staurolite - a red brown to black, mostly opaque, nesosilicate mineral with a white streak.Strain - A change in the volume or shape of a rock mass in response to stressStylolite - an irregular discontinuity or non-structural