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A rock or mineral fragment or a detrital particle of any composition smaller than gravel and larger than a coarse silt grain, having a diameter between 0.003 inches and 0.19 inches (ASTM 2487-85, 1985).


A sedimentary rock composed chiefly of sand-sized grains cemented by calcium carbonate, silica, or other materials.


A typically well-foliated metamorphic rock that splits easily into thin layers or slabs because of the well-developed parallelism of abundant flat or elongate minerals, such as mica and hornblende.


Loose, unconsolidated, fragmental material that originates from weathering of rocks and is transported or deposited by air, water, or ice.

Sedimentary Rock

A rock resulting from the consolidation of loose sediment that has accumulated in layers; also, a rock formed by precipitation from solution, or an organic rock consisting of the remains or secretions of plants and animals.


Eroded soil deposited downslope.


A rock composed primarily of the mineral serpentine, a soft Mg, Fe silicate mineral with a silky luster.


A sedimentary rock composed chiefly of clay and very fine-grained particles of quartz.


A soil particle less than 0.003 inches in diameter that is non-plastic or very slightly plastic and that exhibits little or no strength when air dry (ASTM 2487-85, 1985).


A sedimentary rock composed of silt-sized rock or mineral particles.


Slides are slope movements initiated by outward or downward rupture of displaced material along a well-defined, typically planar or curvi-planar failure surface. Where the geometry of the failure surface is not known, the term slide is applied. Where known, the slide is classified as rotational or translational.

Slope Movement

The gravity-driven gradual or rapid downslope mass movement of soil (earth and/or debris) or rock by falling, flowing, or sliding or by a combination of these movements. The term “slope movement,” rather than "landslide" (Varnes, 1987), is preferred by the NCGS in order to include all mechanisms of slope movement by flowing, falling, or sliding.


A rock composed primarily of the mineral talc, a soft Mg silicate mineral.

Soil Texture

The proportion of sand, silt, and clay.


A Li silicate mineral.


A branch of geology concerned with the definition and description of natural divisions of rock strata, including their history and interrelationships with other rocks.


Any kind of event or action which, at certain levels, causes stress to organisms.


A feature in the rock that results from rock deformation.


The sinking or gradual downward settling of the Earth’s surface, with little or no horizontal motion.


A mineral compound characterized by the presence of SO4.


A mineral compound characterized by joining sulfur with a metal, commonly iron.


A modifier for a rock that contains a visible component of sulfide minerals (e.g., pyrite, pyrrhotite, chalcopyrite).

Surficial Deposit

Unconsolidated and residual, alluvial, colluvial, or glacial deposits lying on bedrock or occurring on the Earth’s surface (see regolith).