Transcript sedimentary rocks - Red Hook Central Schools

Sedimentary Rocks
as the name suggests, form
from sediments, usually deposited
in horizontal layers as seen here
What is a SEDIMENT?
1) Solid particles, such as weathered rock
fragments, plants or animal remains:
sand, clay, pebbles, shells, etc.
small pieces of broken down rocks = clasts
2) Minerals that settle out of solution onto
lake and ocean bottoms, such as rock salt,
dolostone, gypsum
But in order for the sediments to become hard
rock, the particles in the sediment must be
permanently cemented together as seen in this
sandstone
Compaction and
cementation
must both happen
for sedimentary
rock to form.
Minerals like
quartz and calcite
often serve as
the cement
River entering an ocean
Pressure
compacts
The sediments
A conglomerate is formed in a beach environment and
is composed of larger rock sediments from various
origins
Conglomerate boulder
Sedimentary rocks
made of sediment grains (clasts) are called
CLASTIC SEDIMENTARY ROCKS
Sandstone, shale, conglomerate, and
breccia are all clastic sedimentary rocks
Sedimentary rocks like this shale often contain
fossils
Great Salt Lake in Utah
contains many minerals
dissolved in it
If it were to evaporate away, it would leave
behind those minerals in the form of rock salt,
and rock gypsum.
Rocks that form in this way are
called evaporites. They are crystalline.
Limestone and Dolostone can precipitate from
seawater that is warm and shallow
The chalk cliffs of Dover are composed
of a limestone containing microscopic
shells
Sedimentary rocks
that are made up mostly of life forms, like
shells or plant remains, are called
BIOCLASTIC
Limestone and coal are bioclastic rocks
Larger shells are often found in limestone
Millions of years ago lush fern forests dominated the land
As these ferns died, their remains
piled up in large bogs. In many
places the decaying plant remains
became thousand of feet thick
After millions of years and
under great pressure, coal is
the rock that forms from the
remains of these plants
Fern fossils are
often seen on
pieces of coal
How can you tell if a rock is
SEDIMENTARY?
Look for pieces of other rocks (sand grains,
pebbles, etc.)
Does it feel like sandpaper? (sand sized pieces)
Does it feel “dusty” (silt sized pieces)
Does if feel “smooth” (clay or mud)
Look for horizontal layering of the sediments
Look for a fossil
Does it react with acid (Limestone)?
Look for other sed. features (mud cracks,
cross bedding etc.)