Rock - Index Page

Sedimentary Rocks

Sedimentary rocks form in one of three ways:

clastic - from fragments of other rocks that have been cemented together by silica, calcite or iron oxide (shale, sandstone, conglomerate, and breccia)
chemical - from minerals that precipitate (particles fall out of solution & form a solid) as a result of evaporation or chemical reaction (some limestones, rock salt, and gypsum)
organic - from the remains of plants or animals (limestone made of shell fragments and coal)

Sedimentary rocks are distinguished by the types of material and particle sizes that form the rock (shale - sandstone - conglomerate). They often show layers (stratification), may preserve ripple marks or mud cracks, and sometimes contain fossils. Nodules, concretions, and geodes form as liquids deposit silica and calcite in cavities or around organic materials.

Features of sedimentary rocks:

stratification - visible layers of different (size, shape, color, type) sediments
fossils - evidence of plants or animals, including remains and impressions
ripple marks and mud cracks - surface features of the sediments that have been preserved
nodules, concretions and geodes - masses or deposits (of silica or calcite) in sediments

Table of Common Sedimentary Rocks

Sediment Material	Sedimentary Rock	Origin (clastic, chemical, organic)
clay (usually kaolin), silt	shale	clastic
sand grains (usually quartz)	sandstone	clastic
pebbles and sand	conglomerates	clastic
angular fragments of rock	breccia	clastic
sodium chloride precipitating from solution	halite (rock salt)	chemical
tiny grains of calcite deposited from water	limestone	chemical
shells and shell fragments	limestone	organic
compressed plant remains	coal	organic

Some Common Sedimentary Rocks

Clastic

shale	leaf fossils in shale	leaf fossil in shale
sandstone	sandstone	sandstone with fossil

conglomerate	breccia

Chemical

fine-grained limestone	agate (microcrystalline quartz) - forms as dissolved silica gets deposited in rock cavities

Organic

coal	(shell) limestone

Created by M. Clapp
CAM 7/8 Science - BGSD
Modified: 1/6/11

	Sedimentary rocks form in one of three ways: clastic - from fragments of other rocks that have been cemented together by silica, calcite or iron oxide (shale, sandstone, conglomerate, and breccia) chemical - from minerals that precipitate (particles fall out of solution & form a solid) as a result of evaporation or chemical reaction (some limestones, rock salt, and gypsum) organic - from the remains of plants or animals (limestone made of shell fragments and coal) Sedimentary rocks are distinguished by the types of material and particle sizes that form the rock (shale - sandstone - conglomerate). They often show layers (stratification), may preserve ripple marks or mud cracks, and sometimes contain fossils. Nodules, concretions, and geodes form as liquids deposit silica and calcite in cavities or around organic materials.

	Features of sedimentary rocks: stratification - visible layers of different (size, shape, color, type) sediments fossils - evidence of plants or animals, including remains and impressions ripple marks and mud cracks - surface features of the sediments that have been preserved nodules, concretions and geodes - masses or deposits (of silica or calcite) in sediments