Rocks and Minerals - 8.3 Sedimentary Rocks [ARCHIVE] Flashcards
What are sedimentary rocks?
Rocks made from sediments, which need to be cemented together through pressure
What are 3 basic types of sediment, based on where the sediments come from…
-Pieces of weathered rock
-Minerals crystallising from solution
-Dead animals or plant material
What are weathered rock sediments?
The sediments from weathering of rocks (which can come from any type of rock).
What are clastic sedimentary rocks?
Sedimentary rocks formed from weathered rock sediments.
What can you sometimes find within the sediments in clastic sedimentary rocks?
Fossilised remains of long-dead organisms.
What are natural cements?
Chemicals that can flow around the sediments and then set like cement. e.g quartz.
How do chemical sedimentary rocks form?
When dissolved minerals turn into solid crystals and sink to the bottom of a lake, river, or sea. (A.K.A crystallisation).
How do organic sedimentary rocks form?
When dead plant matter or animal debris builds up and is then cemented together.
What are the 3 types of sedimentary rocks?
-Clastic
-Chemical
-Organic
What are the characteristics of clastic sedimentary rocks?
-They have many layers
-The grains don’t interlock
- The rocks may contain fossils.
What are some characteristics of chemical sedimentary rocks?
-They have crystals in them
-They are quite soft
-There is little to no layering in them
-Occasionally fossils
What are some characteristics of organic sedimentary rocks?
-They can be layered
-They are usually soft, although a few such as chert can be fairly hard
What are fossils?
The preserved evidence of organisms that once existed on Earth. To be preserved as a fossil, the dead organism must not be eaten, but decayed slowly.
Why aren’t soft parts found in fossils?
They decay much faster than hard parts (like skeletons, shells etc).
What are the layers in sedimentary rocks called?
Strata (note: Singular layers are called stratum).
