Download 9. Sedimentary Rocks PPT

• Formed from weathered and eroded rock
(sediments) that have been pressed and
cemented together (lithification)
• Most form under water
• Rich in Fossils
Sediments harden into sedimentary rock by
lithification:
• Deposition and Compaction - As layer after layer
of sediments are deposited, the lower layers are
pressed together tightly under the weight of the
layers above.
• Cementing - Some sediments are glued together
by minerals dissolved in water
• Classified by composition
and the manner in which
they formed
3 Categories:
1. Clastic
2. Chemical (Crystalline)
3. Organic (BioClastic)
• Made from broken fragments of other rocks
• Formed from a parent rock being weathered,
eroded, compacted, and cemented (lithification)
into a hard rock.
• Conglomerate = rounded sediments
• Breccia = angled sediments
• Form when dissolved minerals come out of a
solution (ex. Minerals collect when seas or lakes
evaporate).
• They are not made from pieces of pre-existing
rocks (ex. Rock salt or Halite).
• Made from the remains of once-living things. (ex.
Fossil-rich limestone)
• A rock made completely of shell fragments = coquina
•
Microscopic shell pieces = chalk
•
Pieces of dead plants buried under sediments = coal
a) Sandstone is formed from grains of sand pressed
tightly together. Sandstones are very common
rocks. They are formed from the sand on
beaches, in riverbeds, and sand dunes.
Sandstones are usually made of the mineral
quartz.
b) Limestone is formed from tiny pieces of shells
and of dead sea animals that have been
cemented together.
c) Conglomerate contains sand and rounded
pebbles that have also been cemented together.
d) Shale is formed from mud or clay that has been
pressed together. Shale forms in quiet waters
such as swamps and bogs.
Sedimentary rocks can be easy to identify
because you can actually see the layers.