GO 324 Rocks and Minerals
ES 567A Hand Specimen Petrology
Dr. Susan Ward Aber

Emporia State University
Emporia, Kansas USA
Earth Science Department


Ghost Rock, an important landmark for ranchers.
I-70 rest area, milepost 123, in southeastern Utah,
Photo by S.W. Aber, 5/2012.

Introduction to Sedimentary Rock

Introduction    Group    Texture    Composition    Origins
Structures    Classification    References and Links


Sedimentary is taken from Latin sedimentum, which means a settling. These rocks are formed at or near the surface by accumulating particles, which compact, consolidate, and cement into rock layers. As the thickness increases the pressure and rising temperatures compact and cement the particles into rock layers (e.g. mud becomes mudstone and then shale; sand becomes sandstone) (Chesterman, 1978, p. 603). Sedimentary rock usually has bedding or a layered structure and may have fossil remains. While sedimentary rocks and sediments may make up only 0.029% of the total volume of rocks on Earth, they account for two-thirds of the exposed rocks on the Earth's surface (Raymond, 1995, p. 263).

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All sedimentary rock can be divided into one of three groups, depending upon the place of origin or source area of sediments. These groups are detrital, biogenic, and chemical; within biogenic, there are two sediment classifications, organic and bioclastic.
Detrital rock, also called clastic, is formed by the accumulation of sediment from preexisting rocks and minerals, using mechanical weathering and transportation by mechanical agents such as wind, water, ice, and gravity (Chesterman, 1978, p. 603). Biogenic rocks may have organic remains or not and form directly or indirectly by action of plant or animal organisms (p. 604). Chemical rocks form from precipitation from saline or freshwater solution; if the solution becomes concentrated by evaporation, rocks are classed as evaporites (Chesterman, 1978, p. 604). Each group is detailed below.

Detrital sediments, which are also called terrestrial or clastic, are composed of clastic sedimentary particles produced by the weathering and erosion of preexisting igneous, metamorphic, or sedimentary rocks, all derived from land. Detrital texture is described by size (see Wentworth Scale), shape, and composition or the sorting of constituent grains.

I-70 rest area, milepost 115, in southeastern Utah, Red
Ledges at Devil's Canyon http://www.discovermoab.com/
Photo by S.W. Aber, 5/2012.
Biogenic sediments are derived from body parts of organisms. Hard skeletal parts comprise bioclastic biogenic sediments, and soft tissues produce organic biogenic sediments. Bioclastic biogenic sediments are produced by corals, mollusks, brachiopods, echinoderms, sponges, radiolaria, and other marine invertebrates which secrete calcite, aragonite, or silica shells. Such sediments are abundant in shallow, warm, clear seas, and are quickly cemented and may undergo mineralogical and textural diagenesis to create limestone, dolostone, or chert. Organic biogenic sediments are derived from decomposition of plant and animal tissues into carbon or hydrocarbon-rich sediment. Stagnant, oxygen-poor environments are necessary for accumulation of organic sediments. Lithification is accomplished mainly by compaction.

Above - Key Largo Limestone, large branching coral outcrop -
bioclastic biogenic sedimentary rock. Image taken
from academic.emporia.edu/aberjame/ice/lec09/lec9.htm.
Photo by J.S. Aber, 12/1975.

Right - More bioclastic biogenic examples from a Tucson, AZ show
with over sized trilobites, starfish, and other fossil remains in
limestone and shale! Photo by S. Kelley, 2/2008.

Chemical sediments are created by a precipitation of low temperature/pressure minerals from water solution onto a depositional surface or within sediment pores. Depending on the acidity, oxidation, temperature, or salinity, a variety of chemical sedimentary rock may result. Examples of chemical sediments include carbonates, evaporites, opal, chert (may form in other ways too), iron-oxides, and aluminum oxides. Chemical textures are usually crystalline with some special terms, such as oolitic or pisolitic.

Selenite crystals of the Cave of Crystals. Note person for scale
The cave 300 metres (980 ft) below the surface in Naica,
Chihuahua, Mexico. Photo by Alexander Van Driessche, 4/2010,
The example is selenite crystal cave found in a room adjacent to the Naica Mine, where silver, zinc, and lead are mined. An example of the size of one giant crystal is 12 m (39 ft) in length, 4 m (13 ft) in diameter and 55 tons in weight (http://en.wikipedia.org/wiki/Cave_of_the_Crystals). The cave air temperatures are 58 C (136 F) with 90 to 99 percent humidity in this limestone cavern. For more, see Naica Project/Crystals' Cave, http://www.naica.com.mx/english/index.htm; National Geographic (2007), Giant Crystal Cave Comes to Light, http://news.nationalgeographic.com/news/2007/04/photogalleries/giant-crystals-cave/ and http://news.nationalgeographic.com/news/2007/04/070406-giant-crystals.html; Cave of Giant Crystals, Mexico, http://www.crystalinks.com/mexicocrystals.html

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Texture is the size, shape, and arrangement of grains, and it provides a clue to the history of the sediment and its lithification into rock. There are two general categories: clastic and crystalline.

Clastic texture is divided into coarse-grained gravel, medium-grained sand, and fine-grained mud based on the Wentworth Scale (1922) below. Two other ways to show the relationship between sizes of grains are shown on the ternary diagrams below from Shepard (1954) and Folk (1954, 1974). Folk's classification stresses gravel because high amounts in a deposit are a function of high water flow velocity during deposition; Shepard's classification focuses on ratios of sand, silt, and clay because these amounts are a function of sorting and reworking.

Well sorted clastic textures are
even with a uniform grain size;
poorly sorted clastic textures are
uneven with a mix of grain sizes.
Image from http://earthsci.org/education/teacher/basicgeol/sed/sed.html#TexturesofClasticSedimentary

Wentworth Sediment Size Scale (1922)
Size in Millimeters Loose Particle Name Clastic texture terms Consolidated Rock
>256 boulder gravel-coarse grained Conglomerate
64 cobble gravel-coarse grained Conglomerate
4 pebble gravel-coarse grained Conglomerate
2 granule gravel-coarse grained Conglomerate
1.0 very coarse sand sand- medium-grained Sandstone
0.5 coarse sand sand- medium-grained Sandstone
0.25 medium sand sand- medium-grained Sandstone
0.125 fine sand sand- medium-grained Sandstone
0.0625 very fine sand sand- medium-grained Sandstone
0.031 coarse silt mud- fine-grained Siltstone
0.0156 medium silt mud- fine-grained Siltstone
0.0078 fine silt mud- fine-grained Siltstone
<0.0039 clay mud- fine-grained Claystone, mudstone, and shale

Above images taken from
USGS Open-File Report 2006-1195, Nomenclature.

Now it is time to have some fun and check out the micro photography of sand by Dr. Gary Greenberg at http://www.sandgrains.com/. Specifically, find beach sands at http://www.sandgrains.com/Sand-Grains-Gallery.html and moon sands at http://www.sandgrains.com/Moon-Sand-Grains-Gallery.html!

See a 90 second video on sand and promoting the book at http://www.sandgrains.com/Book-Video.html... or if that does not work, http://www.sandgrains.com/sandgrains640x360.mov.

Crystalline texture terms are used for sedimentary rock in chemical and biogenic groups. These terms include rocks that contain whole crystals, fragments of crystals, or fine-grained crystals , which are called smooth or dense such as microcrystalline or cryptocrystalline. For example, cryptocrystalline varieties of quartz are known as chert or chalcedony. Other specialized textural terms include oolitic and pisolitic. For unconsolidated sediment such as sand, the grain shape is also recorded. Shape may be well-rounded, sub-rounded, sub-angular, or angular.

Excellent images demonstrating differences in textures are at

  • http://homepage.smc.edu/grippo_alessandro/rockssedimentary.html, An Introduction to Sedimentary Rocks;
  • facweb.bhc.edu/academics/science/harwoodr/geol101/labs/sediment/Texture.htm, the Earth Science Lab Textures of Sedimentary Rocks;
  • http://geologyclass.org/sedimentary_concepts.htm, Geology Class.org
  • http://facstaff.gpc.edu/~pgore/geology/geo101/sedrx.htm, Pamela Gore.

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    Minerals present in sedimentary rock are largely the remains of or derived from mechanical and chemical transformations of preexisting rock.

    Image taken from a course webpage by David Jessey at

    The minerals may be hard to isolate and identify. Therefore, the composition of the sedimentary rock is given in type terms. Argillaceous is a rock composition primarily made up of clay minerals, while arkosic composition contains grains of feldspars. A sedimentary rock can be primarily feldspar and termed feldspathic. Calcareous contains calcite, and dolomitic contains some calcite as well as calcium magnesium carbonate minerals such as dolomite. A composition rich in carbon and organic matter is termed carbonaceous, while on rich in iron oxides is termed ferruginous. Rocks containing quartz are quartzose, or if free silica, siliceous. Rocks containing nodular chert or chert as replacemnt lenses is simply called cherty.

    Some specific minerals found in different sedimentary rock are shown below.

    Minerals from solution in chemical sedimentary rock include:
    sulfate: gypsum, thenardite
    carbonate: calcite, dolomite
    halide: halite, sylvite, and anhydrite
    borate: borax
    nitrate: trona.

    Minerals formed from preexisting minerals or secondary minerals, oxidized or reduced, and in clastic sedimentary rock include:
    silicate: chrysocolla, hemimorphite
    sulfate: anglesite
    vanadate: carnotite, vanadinite
    carbonate: malachite, azurite, cerussite, smithsonite
    oxide: cuprite
    native element: gold, silver, copper.

    Minerals formed from organic activity include:
    native element: sulfur
    carbonate: aragonite, calcite
    phosphate: apatite
    hydroxide: oolitic limonite.

    Insoluble residue or resistant minerals found in sedimentary rock include:
    silicates: chalcedony, clay minerals
    hydroxides: limonite, bauxite.

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    The environment of deposition is responsible for the character of the sediments that are deposited in a region. Sedimentary depositional environments are classified in two main categories: marine and continental. Continental deposits may be either on dry land such as deserts, gravity, landslides, glacial deposits, or subaqueous such as lake, swamp, steam bed. Sedimentary rocks found within the chemical group may have precipitated origins, such as cave formations and evaporites or hydrothermal replacement deposits such as geysers. Marine deposits include various oceanic environments such as deep ocean, shallow ocean, barrier beach, or coastline with pounding waves. Delta, lagoon, and estuary deposits are transitional between marine and continental.

    Different terms are assigned to different environments. If the sedimentary rock is deposited on land it is continental, but if it is derived from land, terrigenous. If the rock is deposited by water it is aqueous or deposited in sea water, marine. Lacustrine is a rock resulting from lake deposition, and eolian, rock transported and deposited by wind. Hydrogenic is reserved for rock and sediment preciptated from water by inorganic processes.

    For more, see common sedimentary environments and facies at http://earthsci.org/education/teacher/basicgeol/sed/sed.html#SedimentaryFacies

    Photo by S.W. Aber, May 2012. For more information see

    Chert is sedimentary rock that can be grouped under all three categories. Various origins of chert include:

  • bioclastic biogenic when chert contains siliceous skeletond from a biochemical precipitation or a process by which living organisms induce crystallization of solids from solution
  • detrital when chert is formed by compaction of deposits resulting from erosion, transportation, and deposition of previously formed siliceous materials
  • chemical when chert results from hydrogenous precipitation from low temperature water-based solutions that become supersaturated with silica such as vein or cavity fillings in continental or marine rocks, especially volcanics
  • chemical when chert results from hydrothermal precipitation in thermal waters as the solubility of silica increases and silica precipitates upon cooling in hot springs, geysers, and seafloor spreading along mid- ocean ridges
  • chemical when silica replaces calcite in limestones
  • chemical when chert is derived from opaline silica into quartz, nodular or bedded, as a result of diagenesis or chemical conversion
  • Just as chert can have a variety of origins, sandstone and conglomerate are derived from different environments of of deposition. Sandstone types include:

  • Quartzose sandstones are nearly pure quartz (>90%), well sorted deposits with rounded quartz grains, and are usually lithified by cementation with silica, calcite, iron-oxide, glauconite. The environmental conditions could be marine or a coastal environment.
  • Graywacke sandstones are a mixture of quartz, feldspar, mica, rock fragments, and more. They are poorly sorted dirty sandstones with angular grains, lithified by compaction of clayey matrix with an oceanic trench environment.
  • Arkose sandstones are a mixture of quartz and feldspar, variable sorting and angular grains, lithified by cementation with calcite, iron-oxide, or silica. The environmental conditions could be continental alluvial fan or river.
  • More information on features associated with depositional environments see a course webpage from Stephen Nelson http://www.tulane.edu/~sanelson/geol111/sedrx.htm

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    Sedimentary Structures

    Sedimentary rocks are easily recognized in the field by characteristic structural features. If the structures are preserved from the time of deposition, they are called primary structures. These are often related to flowing agents which laid down the sediment or to biological activity at the depositional site. Sedimentary rock is layered or bedded, and this is referred to as strata or stratification. Thin strata is called lamination (e.g., thin-bedded or laminated shale). Other structures include: cross-bedding, ripple marks, cut-and-fill channels, mudcrack casts, concretions, oolites, pisolites, imbrication or an alignment of pebbles, grooves and furrows, rain-drop impressions, fossils in growth position, root casts, and animal burrows.

    Hey, another opportunity for you! If you are enrolled in the course, find an online image demonstrating a sedimentary structure in an outcrop or geologic setting. Send the image and proper citation plus URL to esu.abersusie@gmail.com for one substitution point on exam 3. Place GO 324 point for sed exam in the subject line of the email, and I must receive it by April 21.

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    General Classification

    Texture Cement Clastic Chemical Bioclastic Biogenic Organic Biogenic
    Size/Shape/Sorting Composition Quartz/Chert
    Silica Gel
    Marine Skeletal Organic
    Crystalline Not Applicable (N/A) N/A Limestone/Dolostone
    Rock Salt
    N/A N/A
    Coarse grain size >2mm Silica
    Breccia/Conglomerate Concretions N/A N/A
    Medium grain size >1/16-2mm Silica
    Clean Sandstones
    Greywacke Sandstones
    Arkose Sandstones
    Concretions N/A N/A
    Fine/Very Fine <1/16mm Silica
    Fossiliferous Limestone
    Open Fibrous
    Fossil Remains
    N/A N/A Chalk
    Fossiliferous Limestone
    Dense N/A N/A Anhydrite
    Rock Salt
    N/A Coal: Lignite/

    Visit detailed pictures Rex Elliot's sand collection at http://www.sandcollectors.org/Picture_Gallex.html; Thompson and Cabrol (2009) on texture analysis for planets, http://ml.jpl.nasa.gov/papers/thompson/thompson-ijcaiwais-b-09.pdf; and the USGS website on texture nomenclature, http://pubs.usgs.gov/of/2006/1195/htmldocs/nomenclature.htm. The latter website includes the website images of the Munsell Color Codes, Folk, Shepard, and Wentworth.

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    Recommended References and Notable Links

    To the beginning!

    Petrology Introduction
    Sedimentary Rock
    Metamorphic Rock
    Course Field Trip
    Course Syllabus
    Class and Field Trip Specimen Collection

    This page originates from the Earth Science department for the use and benefit of students enrolled at Emporia State University. The curriculum is © by the author, 2001-2013. Creation and last update May 14, 2013. For more information contact the course instructor, S. W. Aber, e-mail: esu.abersusie@gmail.com.

    To understand copyright, visit www.copyright.gov/. All rights reserved. Susan Ward Aber.