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1
Lab 06 ONLINE
LESSON
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DO TAKE NOTES WHILE PERUSING
ALONG…
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Sedimentary Rocks
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As we saw last time, a rock is a
collection of minerals…
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There’s a mineral
There’s a mineral
There’s a mineral
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A sedimentary rock is comprised of
pieces of other rocks called sediment…
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There’s a sediment
There’s a sediment
There’s a sediment
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The Rock Cycle tells us that rocks first start out as igneous rocks…
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Eventually, these rocks undergo changes…
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Weathering is the process of breaking up rocks…big rocks turn into small rocks
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Sediment (small rocks) is transported and deposited where it forms into sedimentary rock…
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So a sedimentary rock is just a
collection of rock particles called
sediment…
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Weathering is the process of breaking
rocks apart…
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There are two types of weathering…
Chemical
Mechanical
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Chemical weathering is
caused by chemicals that come
in contact with minerals……
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One chemical is water…
H2O
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Water will come in contact with halite…
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Water will break up the halite…
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Halite is broken down into its constituent elements of sodium (Na+) and chloride(Cl-)
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This is chemical weathering…
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Another example of chemical
weathering…
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CaCO3 + H2CO3- →
Ca2+ + 2HCO3-
Acids will break down minerals……
calciteCarbonic Acid
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Calcite plus carbonic acid will break down to form calcium and
bicarbonate…
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Mechanical Weathering is
caused by mechanical actions
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In other words…rocks are broken
down by a pushing, pounding or scraping
force…
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Frost Wedging = low atmospheric
temperatures will break up rocks
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Water in cracks will freeze causing the expanding water to break up rocks…
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The result is sediment
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Landslides are another form of
mechanical weathering…
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Rocks under the force of gravity will fall down and break up on impact with
the ground…
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Punch the dinosaur to see a video of some jokers producing an artificial
mechanical weathering
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Did you see that? A large sandstone was
pushed over the cliff…fell and broke into smaller rocks…
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Mechanical weathering in action!
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So, weathering breaks up rocks…by the way, these rocks
are generally referred to as Clastic
Sedimentary Rocks…
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Clastic meaning that rocks are broken up
into fragments…
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So how do sediments make
rocks?
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In addition to weathering…
transportation, deposition and lithification of
sediments must take place…
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Transportation is the movement of sediment…
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Streams are a common mechanism of
transportation…
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Stream is just another word for a river…
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Streams can carry large quantities of sediment…as long as streams move,
sediment is transported…
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Streams move…sediments move…
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However, once a stream stops moving, then
sediments will be deposited…
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Deposition occurs when a mechanism
of transportation stops…
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Streams stop…sediments dropout of moving water…
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Deposition occurs…
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The result….
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A sedimentary rock…
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Such as this sandstone…
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It is made out of sand…
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It is a result of mechanical
weathering…
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transportation…
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and deposition…
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Once sediment has deposited…it then
undergoes lithification
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Lithification is the process of turning
loose sediment into a solid rock…
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Lithification involves cementation and
compaction
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Compaction
Sediment is pushed together
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Cementation
A binding agent is introduced…
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Cementation
to glue sediment together
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SEDIMENT
CEMENT
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Cementation process utilizes…
CaCO3
SiO2
Fe2O3
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These are binding agents…That form
Clastic Sedimentary Rocks
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Characteristics of clastic sedimentary
rocks…
GRAIN SIZE
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Sediments are formed into a number of sizes…
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Sizes are listed in metric form
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So grain size is used to categorize sedimentary rocks…
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A rock with grains 2mm in size is called a sandstone…
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A rock with grains 1/256 mm in size is called a shale…
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A rock with a larger grain size is called a Breccia or Conglomerate…
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Breccia and conglomerate are based on the roundness of
sediments...
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Characteristics of clastic sedimentary
rocks…
SORTING
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Sorting is the arrangement of the
grains of sediment…
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Sorting
A collection of very large and very small grain sizes
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Sorting
A collection of less differing grain sizes
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Sorting
A collection of almost the same sized grains
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Sorting is an indicator of the
speed of a stream
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A fast stream produces a well
sorted sediment…
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A stream of fluctuating speeds produces poorly
sorted sediments…
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Characteristics of clastic sedimentary
rocks…
ROUNDING
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Rounding refers to the degree to which sharp corners have been worn away…
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Rounding
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Rounding
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Rounding
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Rounding indicates the amount of
transportation a sediment has
undergone
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The more transportation, the
smoother the grain…less
transportation, the more angular the
grain…
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Another form of sedimentary rock are Biochemical
Sedimentary Rocks…
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Biochemical sedimentary rocks are made up of the remnants of once living organisms…
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Here is a coquina…
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It is made up of shell fragments of marine
organisms…
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Some biochemical rocks contain
invisible fragments…
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Such as this chalk
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Some biochemical rocks react with acid
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REVIEW
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Sedimentary Rocks are made of sediment…
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Sediment is a result of
Chemical weathering
Mechanical weathering
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Sedimentary Rocks are grouped into
Clastic
Biochemical
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Characteristics of clastic sedimentary
rocksSorting
Rounding
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Sorting
Well sorted
Moderately sorted
Poorly sorted
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Rounding
Very angular grains
Subangular grains
Well rounded grains
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Grain Size
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A note:
Terms such as aphanitic, phaneritic
and so on are not applied to
sedimentary rocks…
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It is now time for a short assignment….ask Bob for
a worksheet…
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