Transcript Sedimentary Rocks website

- 75% of the rocks exposed at the
surface are sedimentary rocks.
- sediments are loose materials such as
rock fragments, mineral grains, and bits of
plant and animal remains that are moved
by wind, water, ice, or gravity.
- sedimentary rock forms when sediments
are pressed and cemented together, or
when minerals form from solutions.
- sedimentary rocks often form in
layers
- older rocks are usually found at the bottom
layers, however, sometimes forces within Earth
overturn layers of rock, and the oldest are no
longer at the bottom.
- sedimentary rocks are usually
classified as detrital, chemical or
organic.
► detrital
= clastic
► chemical and organic = nonclastic
► * you need to know all of these terms!!!
- Detrital sedimentary rocks: made
from broken fragments of other rocks
1. when rock is exposed to air, water, or
ice, it is unstable and breaks down. This
process, which breaks rocks into smaller
pieces, is called weathering.
2. when layers of small sediments
stick together because of pressure,
compaction occurs.
3. when water and other minerals (such
as quartz, calcite and hematite, which act
as naturally glues) move through open
spaces between larger sediments, gluing
them together, cementation occurs.
4. Detrital rocks have granular textures,
much like granulated sugar. They are
named according to the shapes and sizes
of the sediments that form them.
Breccia: angular
Conglomerate: rounded
► Big
Sediments
Conglomerate (round pebbles)
 boulders
 pebble
 gravel
 sand
 silt
 clay
sandstone (feels sandy, has pores)
shale (feels smooth, pressure from layers)
Small Sediments
Chemical sedimentary rocks: form
when dissolved minerals come out of
solution.
- chemical sedimentary rocks are different:
they are not made from pieces of
preexisting rock.
- limestone: when calcium
carbonate comes out of solution in
the form of calcite
- limestone is usually deposited on
the bottom of lakes or shallow seas.
- large areas of the central U.S. have
limestone bedrock because seas covered
much of the country for millions of years.
- The mineral halite forms rock salt
when water that is rich in dissolved salt
evaporates.
Michigan Basin
- companies mine deposits of rock
salt as an important resource.
- Organic Sedimentary Rocks: made
from remains of once-living plants or
animals.
- fossil-rich limestone: similar to chemical
limestone (both made of calcite) however,
fossil-rich limestone mostly contains
remains of once-living ocean organisms
instead of only calcite.
- chalk is made of microscopic
shells.
- coal is made of plant remains,
chemically changed by microorganisms
compacted over millions of years.
- The rock cycle is a continuous and
dynamic process.