Transcript Sedimentary Rocks

Sedimentary Rocks
•Rocks that form by
the compaction and
cementation of
sediment that
transform sediment
into solid rock are
sedimentary.
Sedimentary Rocks
• Geologists estimate that sedimentary
rocks account for only 5% (by volume)
of the Earth’s outer 16 km but they make
up 75% of the rocks exposed as
outcrops at the surface of the Earth.
Lithification – the process of turning
loose sediment into stone.
1. Compaction – as sediments accumulate
through time, the weight of the overlying
material compresses the deeper sediments
until they harden.
2. Cementation – cementing material through
time precipitate on to the sediment, filling the
spaces and joining the particles, Calcite,
silica and iron oxide are the most common
cements.
Sedimentary rocks
• There are two classes of sedimentary
rocks.
1. Clastic (detrital) – formed by the
lithification of sediment formed by
weathering, erosion and mass wasting.
Example - sandstone
2. Chemical sedimentary rocks
– rocks that formed when soluble
material dissolved in lakes or seas
precipitates out and hardens.
Example - gypsum
Classification of Sedimentary rocks
Clastic rocks
• Clastic sedimentary rocks are classified
by their grains size.
• Siltstone – gritty between the teeth
• Sandstone – feels like sand.
• Conglomerate –rounded thumbnail size
and larger
• Breccia – angular thumbnail size and
larger.
Chemical sedimentary
(sometimes called precipitates or
evaporites.)
• These rocks have a crystalline
structure. Same shape, same
color, same size crystals. (Note –
These are not interlocking crystals like
igneous rocks.)
• They can be called biochemical if they
have organic material in it.
Identification Clues
• Sedimentary
rocks can be
found in layers.
• Example sandstones.
• They are
sometimes soft.
• example gypsum.
Identification clues Continued
• They may
contain fossils.
• Example –
limestone
• They look like a
broken rock
stuck together.
• Example conglomerate