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30 terms

Sedimentary rocks

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Detrital
Consist of particles (sediment) broken off of preexisting rocks (conglomerate, breccia, sandstone, siltstone, shale)
Chemical
Consist of previously dissolved substances that precipitated from water (limestone, marl, coquina, chalk, gypsum, rock salt, dolostone, chert)
Conglomerate
Composed of rounded particles 2 mm or larger in diameter; commonly cemented by hematite, silica, or calcite; may be of any particle composition
Breccia
Same as conglomerate, but angular particles
Sandstone
composed of rounded or angular sand particles
Siltstone
composed of silt particles, gritty texture
Shale
compacted clay and silt; fissle (splits into thin sheets); most common detrital sedimentary rock
Limestone
Inorganic or organic (usually organic); the consolidated equivalent of limey mud, calcareous sand, and or shell fragments; abundant calcium carbonate; freely effervescent in hydrochloric acid; the most abundant chemical precipitate
Marl
Inorganic or organic; calcareous mudstone; often beige in color
Coquina
Organic form of limestone; visible shell fragments
Chalk
Organic form of limestone; microscopic shells (coccoliths); used on blackboards; often white in color; often scratched by fingernail
Gypsum
Inorganic; hydrous calcium sulfate in rock form; scratched by fingernail
Rock salt
Inorganic; sodium chloride (halite) in rock form; tastes salty
Dolostone
Inorganic or organic; contains 50% or more of the mineral dolomite; reacts with HCl only if powdered
Chert
Inorganic or organic; cryptocrystalline silica (quartz); conchoidal fracture; scratches glass
Sedimentary Rocks
5% of the volume of outher 10 mi of crust. 75% on the continents.
How sedimentary rocks formed can be determined by
texture & mineral composition
Particles
Sediment
Inorganic Chemical
Consist of minerals that precipitate directly from water without the action of living organisms. Evaporation is often a cause.
Organic Chemical
include remains of plants or animals, such as skeleton or shell fragments
Lithification
converts sediment into rock. Compaction caused by pressure generated from weight of overlying sediment. Cementation is binding of sediment by mineral agents. Common cementing agents hematite, limonite, calcite and silica
Texture refers to
size, shape and sorting of particles that make up the rock
Size
Large particles suggest high energy levels in the environment of deposition. For example, powerful water currents in a mountain stream could carry cobbles and boulders, but these would probably not be found in the middle of a lake, with weaker currents.
Shape
Rounding of individual particles. well-rounded particles = long transport history. Angular with sharp edges = short transport history.
Sorting
well-sorted detrital rock contains particles about the same size, poorly sorted = lots of different sizes. Wind is best sorting agent, transporting mainly silt particles. Ice is poorest, carries all particle sizes
Stable minerals
last a long time at earth's surface. Quartz and hematite
Unstable minerals
Tend to weather away faster.
Red vs. black
Red contain iron oxide, which forms in oxygen-rich environments. Black have lots of organic matter, oxygen deficient environments
Meander
curve in a river
Delta
sediment accumulation at mouth of river