Where do sedimentary rocks originate?
How are they formed?
What are the three categories of sedimentary rocks?
What are the distinguishing characteristics between the three categories of rocks?
(Broken Link Removed)
http://geology.com/rocks/sedimentary-rocks.shtml
http://en.wikipedia.org/wiki/Sedimentary_rock
What are the three categories of sedimentary rocks?
clastic rock formed from fragments broken off from parent rock, by
o weathering in situ or
o erosion by water, ice or wind
followed by transportation of sediments, to the place of deposition;
biogenic activity; or
precipitation from solution.
The sediments are then compacted and converted to rock by the process of lithification
This is from the second link above:
"There are three basic types of sedimentary rocks:
1) clastic sedimentary rocks such as breccia, conglomerate, sandstone and shale, that are formed from mechanical weathering debris;
2) chemical sedimentary rocks such as rock salt and some limestones, that form when dissolved materials precipitate from solution; and,
3) organic sedimentary rocks such as coal and some limestones which form from the accumulation of plant or animal debris."
Sedimentary rocks originate from the accumulation and lithification (compaction and cementation) of sediments.
To understand how sedimentary rocks are formed, we need to look at the process of sedimentation. Sedimentation occurs when weathering and erosion break down rocks into smaller fragments or dissolve them into water. These sediments are then transported by wind, water, or ice and eventually settle down in areas such as rivers, lakes, or ocean basins. Over time, as more and more sediments are deposited, the weight of the overlying layers compresses the lower layers, leading to compaction. This compaction reduces the pore spaces between the sediment grains and increases their density. As water passes through the sediment, minerals dissolved in the water can precipitate, acting as cementing agents and binding the sediment grains together. This process is known as cementation. Eventually, these layers of sediment become rock through a process called lithification.
There are three primary categories of sedimentary rocks: clastic, chemical, and organic.
1. Clastic sedimentary rocks are composed of fragments derived from pre-existing rocks. These fragments, known as clasts, can range in size from microscopic clay particles to large boulders. Examples of clastic sedimentary rocks include sandstone, shale, and conglomerate.
2. Chemical sedimentary rocks form when dissolved minerals precipitate out of water. This can occur through processes like evaporation, as seen in the formation of rock salt or gypsum, or through the accumulation of shell fragments to create limestone.
3. Organic sedimentary rocks are formed from the remains of dead plants and animals. Over time, these organic materials can be compacted and undergo chemical changes to form rocks such as coal, oil shale, and chalk.
The distinguishing characteristics between these categories of sedimentary rocks lie in their composition, texture, and origin. Clastic rocks exhibit varying grain sizes and may contain visible fragments of different rock types. Chemical rocks often have a crystalline texture due to the precipitation of minerals from solution, while organic rocks may retain the structure or texture of the organisms from which they formed. These characteristics provide clues about the environment and processes involved in their formation.