Detrital and chemical and organic sediment rocks, formed from the erosion, transportation, and deposition of pre-existing rocks
DETRITAL Sedimentary Rocks: formed from erosion and transportation of a pre-existing rock
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ROCK
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COMPOSITION
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SIZE/SHAPE
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SORTING
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ORIGIN
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Quartz Sandstone
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quartz (white to tan); fossils (invertebrates, vertebrates, plants)
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medium-grained; rounded (sandstone) or angular (gritstone)
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well-sorted
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marine (continent shelf or slope); coastal (delta; beach/barrier island; tidal flat); continental (stream channel, if rippled; desert; lake)
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Shale
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clay (too small to see); fossils (invertebrates, vertebrates, plants)
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clay-sized (feels smooth); angular (too small to see)
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well-sorted
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marine (continental shelf or slope, deep marine); coastal (delta, tidal flat); continental (stream floodplain)
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Siltstone
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clay and quartz (usually too small to see); fossils (invertebrates, vertebrates, plants)
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silt-sized (feels gritty); angular (too small to see)
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well-sorted
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marine (continental shelf or slope, deep marine); coastal (delta, tidal flat); continental (stream floodplain)
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Graywacke
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quartz and rock fragments mixed with clay; often gray colored
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sand-sized (visible grains up to 2 mm); rounded to angular
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moderate sorting
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marine (continental shelf: cross-beds, ripple marks common)
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Arkose
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feldspar (usually orthoclase), quartz, and other minerals
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sand-sized (visible grains up to 2 mm); angular; cross-beds
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moderate to poor sorting (few grains >2 mm)
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continental (alluvial fan); considered an immature rock because of high feldspar contnt; derived from granite disintegration
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Breccia
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fragments of any rock type
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gravel-sized (> 2 mm); angular; cross-beds
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moderate to poor sorting
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marine; continental (alluvial fan); coastal (especially where mechanical weathering is active)
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Conglomerate
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fragments of any rock type
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gravel-sized (> 2 mm); angular to rounded; may have scratches
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moderate to poor sorting
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continental (stream channel; glacier; lake, near shore)
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CHEMICAL & ORGANIC Sedimentary Rocks:
organic sediments form from biological activity; chemical sediments form by primary precipitation in shallow marine environments
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ROCK
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COMPOSITION
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SIZE
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TEXTURE
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ORIGIN
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Chalk
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calcite (acid reaction)
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fine-grained; powdery; soft
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black, gray, or white); earthy smell
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marine (continental shelf, during the Cretaceous period)
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Coquina
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calcite (acid reaction)
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shell fragments loosely cemented with very little matrix
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coastal (beach/barrier island; tropical beaches)
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Crystalline Limestone
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calcite (acid reaction); fossils (invertebrates, coral, algae)
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medium to coarse (visible) grains
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crystalline
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marine (continental shelf)
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Fossiliferous Limestone
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calcite (acid reaction); fossils (invertebrates, coral, algae)
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fine to coarse grains
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crystalline matrix
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marine (coral reef)
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Micrite
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calcite (acid reaction)
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fine grains (too small to see)
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crystalline
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Oolitic Limestone
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calcite (acid reaction); fossils (invertebrates)
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sand-sized
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spheres (ooliths) packed together
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marine (continental shelf; warm, shallow, strongly agitated marine conditions)
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Chert
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quartz (scratches glass)
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fine grains (too small to see)
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grayish in color; cannot be scratched with a knife; conchoidal fracture
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marine (deep marine: seabeds)
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Rock Gypsum
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gympsum
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fine to coarse grains
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crystalline (vitreous luster); fibrous; distorted bedding; soft (can be scratched with a fingernail); uneven fracture
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marine (arid, hot, restricted circulation); found with sandstones, marls, limestones
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Rock Salt
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halite; impurities of clay minerals and iron oxides (reddish brown)
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fine to coarse grains
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crystalline
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marine (arid, hot, restricted circulation); saline waters (salt lakes)
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Coal (bituminous and anthracite)
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plant remains (carbon)
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dense, black masses; depending on grade, may be dull to vitreous; lower grades may contain minor fossils
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swamp |
Peat
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plant remains (carbon)
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fibrous, brownish plant material; swamp
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swamp
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