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  • A fracture surface or zone of fractures in Earth materials along which there has been vertical and/or horizontal displacement or movement of the strata on opposite sides relative to one another.
  • A mnemonic adjective derived from feldspar + lenad (feldspathoid) + silica + c, and applied to an igneous rock having abundant light-colored minerals in its mode; also, applied to those minerals (quartz, feldspars, feldspathoids, muscovite) as a group. It is the complement of mafic.
  • Containing iron and magnesium; applied to mafic minerals.
  • Any sediment deposited by an agent so as to fill or partly fill a valley, a sink or other depression.
  • A general term for the property possessed by some rocks of splitting easily into thin layers along closely spaced, roughly planar, and approximately parallel surfaces, such as bedding planes in shale or cleavage planes in schist; its presence distinguishes shale from mudstone. The term includes such phenomena as bedding fissility and fracture cleavage.
  • A relatively wide planar opening in bedrock that originated as a fracture or fault. The opening may be partially or totally filled with soil or, if open, can act as a conduit for flowing water.
  • Said of rock that tends to split into layers of suitable thickness for use as flagstone.
  • The surface or strip of relatively smooth land adjacent to a stream channel produced by the stream's erosion and deposition actions; the area covered with water when the stream overflows its banks at times of high water; it is built of alluvium carried by the stream during floods and deposited in the sluggish water beyond the influence of the swiftest current.
  • Of or pertaining to a river or rivers.
  • (a) A very common mineral of the apatite group: Ca5(PO4) 3F. It is a common accessory mineral in igneous rocks. Syn: apatite. (b) An apatite mineral in which fluorine predominates over chlorine and hydroxyl.
  • Sedimentary deposits formed by a combination of fluvial (river) and lacustrine (lake) conditions.
  • The basic rock unit distinctive enough to be readily recognizable in the field and widespread and thick enough to be plotted on a map. It describes the strata, such as limestone, sandstone, shale, or combinations of these and other rock types. Formations have formal names, such as shale, or combinations of these and other rock types formations have formal names, such as Joliet Formation or St. Louis Limestone (Formation), generally derived from the geographic localities where the unit was first recognized and described.
  • Any remains or traces of a once-living plant or animal preserved in rocks (arbitrarily excludes Recent remains); any evidence of ancient life. Also used to refer to any object that existed in the geologic past and for which evidence remains (for example, a fossil waterfall).
  • Said of a rock or mineral that crumbles naturally or is easily broken, pulverized, or reduced to powder, such as a soft and poorly cemented sandstone.