Sedimentary rocks

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30 terms

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

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