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Sedimentary Rocks
Chemical Sedimentary Rocks
Limestone
Chert – Silica
Evaporites
Organic Rocks
Coal
Oil and natural gas
Chemical Sedimentary Rocks
Clastic Sedimentary Rocks
Formed from clasts (bits and pieces
of pre-existing rocks) transported,
deposited,and lithified
Chemical Sedimentary Rocks
Formed from precipitation of minerals
within the depositional basin. Includes
biominerals, evaporites, coal, chert, etc.
Evaporites
minerals precipitated from
evaporating water
Siliceous Rocks
Silica and opalline silica
precipitate either organically or
inorganically
Coal and Peat
Carbon-rich deposits formed from
build-up of plant material in
swamps
Carbonates
Variety of limestones composed
of calcite, aragonite, and dolomite
precipitated either organically or
inorganically
http://csmres.jmu.edu/geollab/Fichter/SedRx/chembiokey.html
Common Minerals:
Carbonates - Limestone
Biochemical (corals)
Bioclastic (chalk, coquina)
Inorganic – chemical precipitate
travertine
tufa
oolitic limestone
Calcite CaCO3
Aragonite CaCO3
Dolomite (CaMg)CO3
Corals and Snails
Limestone
Unlike other chemical sedimentary rocks,
limestone is usually formed from loose
sediment similar to clastic sediment. These
kind of limestone are sometimes called
bioclastic.
It is therefore relatively easy to mistake
limestone for a clastic rock unless you
perform an acid test. Carbonates will react
with acid; clastic sediments will not.
Calcite and aragonite react energetically
with rather weak acid. Dolomite will react
sluggishly, and usually needs to be ground
up to see a reaction with weak acid.
Snails
Some algae precipitate aragonite flakes and needles as
skeletons. When they die, the skeletal bits become sandand mud-sized carbonate sediment.
http://www.turtles.org/
http://www.geo.mtu.edu/FIELD_TRIPS/florida/
Lime mudstone - limestone
with mud-sized carbonate
grains. Comes in many
different colors, and
frequently contains fossils.
http://www.ndc.edu/stones/newpage16.htm
http://seis.natsci.csulb.edu/bperry/Sedimentary%20Rocks%20Tour/biochemical_sedimentary_rocks.htm
Underwater dunes formed
from carbonate sediment
Fig. 06.22a
Stony corals precipitate sometimes
massive aragonite skeletons, which
break up to form boulder- to mudsized carbonate sediment.
Fringing coral reef around a island. As the volcanic island sinks,
the coral growth keeps up, eventually forming a coral atoll.
Chalk
Limestone formed from
the microscopic calcite
skeletons of tiny animals.
http://earthobservatory.nasa.gov/Library/Coccolithophores/
Shell Coquina
Shells cemented together with little or
no matrix
http://www.dep.state.fl.us/geology/geologictopics/rocks/anastasia.htm
Inorganic Carbonates
Limestone precipitated from dissolved ions in water,
including:
Seawater
Hot springs
Groundwater
Evaporating basins
Pore water
Dissolved Solids in Thermopolis Hot Spring
Total Dissolved Solids 2373
Hydrogen Sulfide (H2S) 4.5
“Hardness” (CaCO3) 1274
Thorium less than 0.6
Bicarbonate (HCO3) 755
Silica (SiO2) 82
Iron (Fe) 03
Lead 0.004
Magnesium (Mg) 76
Sodium (Na) 262
Potassium (K) 49
Sulfate (SO4) 760
Chloride (Cl) 328
Fluoride (F) 3.7
Nitrate (NO3) 10
Strontium 20
Lithium 2
Barium 2
Aluminum 1
Chromium trace
Calcium (Ca)
Boron 0.56
Manganese 0.02
Titanium 60
Zinc 2
Tungsten 0.01
Vanadium 0.1
Copper trace
http://www.thermopolis.com/
Siliceous Sedimentary Rocks
Microcrystalline quartz and opal precipitated from dissolved ions in
sedimentary environments. Can be precipitated organically or inorganically.
Microcrystalline quartz can also precipitate in pore spaces to form cement.
http://www.diskworks.com/octoberopals/opal1.html
Scanning Electron Micrograph (SEM) of tiny, siliceous
skeletons of radiolarians, which are a source silica chert
Chert nodules
common occurrence of chert
in other sedimentary rocks
(this is limestone)
Fig. 06.23a
Bedded Chert
Another common mode of
occurrence in sedimentary
deposits.
Evaporites
Minerals (halite, gypsum,
sylvite etc.) precipitated from
dissolved ions in basins from
which water is evaporating.
Evaporite Production
H2O
H2O
H2O
Evaporation
1000 ft
Example: Minerals formed from dissolved ions
as seawater evaporates
Ionic Composition of Seawater
Cations
Anions
Na
Na+
10,556
Mg2+
1,272
ClCl
(SO
SO44)2-
K+
K
Ca2+
Ca
380
(HCO3)- 140
400
parts per million
Common Mineral Salts
NaCl - Halite
KCl - Sylvite
CaSO4•H2O - Gypsum
18,980
2,649
Total
Ions:
H22O:
H
O
34,387 ppm
965,613 ppm
35 o/oo
normal marine salinity
Other Mineral Salts
KMgCl3•6H2O - Carnalite
MgCO3 - Magnesite
CaMg(CO3) - Dolomite
CaSO4 - Anhydrite
Basin of Seawater
H2O
H2O
H2O
Evaporation
As the water evaporates, the
ions become more
concentrated, and different
minerals precipitate.
1000 ft
15 ft
2.6 ft.
Sylvite (KCl) and Mg-salts
11.8 ft.
Halite - NaCl
0.5 ft.
Gypsum - CaSO4
Shores of the Great Salt Lake, Utah
http://speclab.cr.usgs.gov/PAPERS.calibration.tutorial/
Coal
Sedimentary rock formed from
the remains of plant material
Coal comes in various grades,
depending on the amount of
post-depositional alteration:
Peat
Lignite
Bituminous coal
Anthracite (a metamorphic rock)
http://geoinfo.nmt.edu/education/litegeology/images/coal.gif
Coal is formed from swamp deposits
It is derived from woody plants
The buried material is compressed and heated in the
Earth, driving off the water, increasing the carbon content.
Higher carbon content = higher grade fuel
Coal almost always contains pollution-causing impurities.
http://www.fmnh.org/
coal bed
Oil and Natural Gas
Formed when microscopic
organisms die and accumulate in
an area of low oxygen, preserving
organic matter.
When sediments are compacted
and heated, organic matter is
transformed into hydrocarbons,
producing oil and natural gas.
http://www.sohoblues.com/GulfWarWeb/previewpages/previewpage5.htm