Answer:
A.sadimoentary rocks
Explanation:
Sedimentary Rocks
Igneous rocks are sometimes considered primary rocks because they crystallize from a liquid. In that case, sedimentary rocks are derived rocks because they are formed from fragments of pre-existing rocks.
Formation of Sedimentary Rocks
Sedimentary rocks are the product of 1) weathering of preexisting rocks, 2) transport of the weathering products, 3) deposition of the material, followed by 4) compaction, and 5) cementation of the sediment to form a rock. The latter two steps are called lithification.
Weathering
When rocks (igneous, sedimentary, or metamorphic) are at or near the surface of the earth they are exposed to the processes of weathering.
In mechanical weathering rocks are broken up into smaller pieces by frost-wedging (the freezing and thawing of water inside cracks in the rock), root-wedging (tree and other plant roots growing into cracks), and abrasion caused by, for example, sand-blasting of a cliff face by blowing sands in the dessert, or the scouring of water transported sand, gravel, and boulders on the bedrock of a mountain stream. Mechanical weathering breaks rocks into smaller and smaller pieces but without otherwise altering the minerals.
In chemical weathering minerals are changed into new minerals and mineral byproducts. Some minerals like halite and calcite may dissolve completely. Others, especially silicate minerals, are altered by a chemical process called hydrolysis. Hydrolysis is the reaction of minerals in weakly acidic waters. Most natural surface waters are slightly acidic because carbon dioxide from the air dissolves in the water. Some of the dissolved CO2 reacts with the water forming the chemical compound carbonic acid.
Complete weathering of silicate rocks will yield:
solid materials
1) clays
2) quartz sand (if the rock originally contained quartz)
dissolved materials
3) soluble silica
4) metal cations
Rock fragments will also remain where the rocks are not completely weathered.
Not only is quartz the most stable of the common rock forming minerals in chemical weathering, its high hardness and lack of cleavage make it quite resistant to mechanical weathering. Quartz is itself an agent of mechanical weathering in the form of blowing dessert sand.
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