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8/3/2019 Chemical and Biochemical Rocks
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Keenan
Veneracion
Kristia
Alcantara
CHEMICAL AND
BIOCHEMICAL ROCKS
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Minerals INSOLUTION
Not dependent on
currents or energyParticle size is not
important inclassification
Classified on thechemistry of thedominant minerals
CHEMICAL AND BIOCHEMICAL
ROCKS
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- forms when minerals that are dissolved in
a solution crystallize.
Examples:
Inorganic limestone
Chert
Rock salt
Gypsum
CHEMICAL ROCKS
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Composed of the mineral calcite (CaCO3 -
calcium carbonate), and are thus all known ascarbonates.
F
ormed when calcite that is dissolved in lakes,seas, or underground water comes out of solution and forms crystals
Tends to be mixed together in variouscombinations in the rocks.
Are extremely abundant and important(ex:construction materials, abrasives, agriculturalsoil treatments, construction aggregates,pigments, pharmaceuticals and more)
INORGANIC LIMESTONE
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Limestone Dolomite
IMAGES OF CARBONATES
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Composed of SiO2
Forms from the recrystallized skeletons of
"animals" (single celled radiolarians, and glass
sponges) or single celled "plants" (diatoms,silicoflagellates)
Although the silica comes from skeletons, to
become chert it must be chemically recrystallized,
thus putting it in the chemical category
CHERT
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CHERT
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Rock salt (hali te; NaCl) and gypsum/alabaster (CaSO4 .
H2O)
Originally are dissolved in the sea water, making the sea
salty
When sea water evaporates in a closed area, such as a
lagoon, the salt concentration becomes very high,
supersaturated, and precipitates out
The process is common in desert areas, with examples
today in the Red Sea and Dead Sea in the Middle East, both
highly saline.
Normal ocean waters conta in about 34,500 ppm TDS (Total
Dissolved Solids). If the concentration reaches about
100,000 ppm TDS, then gypsum wil l begin to precipitate
from the water. At a salinity of 350,000 ppm, Halite wil l
begin to precipitate.
EVAPORITE ROCKS
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Rock Salt (halite) Gypsum
IMAGES OF EVAPORITES
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- Forms when the remains of plants andanimals are deposited in thick layers. Theterm organic refers to substances that were
once part of living things or were made byliving things.
- Examples:
Biochemical limestone
Peat
Coal
BIOCHEMICAL ROCKS
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The hard shel ls of l iv ing th ings produce some k inds of l imestone.
In the ocean, many l iv in g things including coral, c lams, oysters, andsnai ls , have shel ls or skeletons made of calc i te. W hen these animalsdie, their shel ls p i le up as sediments on the ocean f loor.
Over mil l ions of years, these layers of sedim ents can grow to a depth of hundreds of meters.
Slowly the pressure of overlying layers compacts the sedim ents.
Some of the shel ls d issolve, forming a solut ion of calc i te that seeps intothe spaces between the shel l f ragments.
Later, the dissolv ed material comes out of solut ion forming calci te.
The calc i te cements the shel l par t ic les together forming inorganicl imestone.
BIOCHEMICAL LIMESTONE
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BIOCHEMICAL LIMESTONE
An organic limestone
organisms with shells or
skeletons
death
Shells or skeletons piling up as
sediments; compacted by pressure
of overlying layers
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A plant matter that is par tially decomposed under conditions of no oxygen.
When dug from the ground, peat is about 75 percent
water by weight; once dried it is about 60 percentcarbon and makes a useful fuel in many regions.
Peat forms large and widespread deposits in thenorthern latitudes, where wet ground (peat bogs andfens) and abundant plant growth favor its preservation.
Peat turns slowly into coal with burial and pressure asgentle heat drives out light hydrocarbons. Thesevolatile compounds become petroleum.
PEAT
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Uses of Peat: horticultural and agricultural uses; energy
uses
Unlike all the other chemical/biochemical rocks, peat and
coal always form in the presence of clastic rocks -
sandstones and shales
PEAT
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Forms from the remains of swamp plants buried in water
As layer upon layer of the plant remains build up, the weight of the layers squeezes the decaying plants.
Then over mill ions of years, they slowly change into coal.
Uses of Coal: energy uses (mainly as fossil fuel)
Bituminous coal
COAL
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http://www.windows2universe.org/earth/geology/sed_chemic
al.html
http://cmsc.minotstateu.edu/Labs/rockslab/sedimentary/Che
mical%20sedimentary%20rocks.html
http://csmres.jmu.edu/geollab/fichter/SedRx/sedclass.html
'Prentice Hall Exploring Earth Science '
(1995; Prentice Hall)
SOURCES