[Geography Notes] on Siliceous Rock Pdf for Exam

Any rock belonging to the group of sedimentary rocks that largely or entirely consists of silicon dioxide (SiO₂) in either of the two forms of quartz or amorphous silica and cristobalite is widely known as siliceous rock. In the class of the sedimentary rocks, the rocks that are formed as a result of the chemical precipitation are included in the category and examples of siliceous rock or silica rock, as it contains silicon dioxide as the main constituent. This siliceous sedimentary rock does not include any rock that is formed due to detrition or fragmentation.  

Classification of Rocks

Rocks are an integral part of the Earth’s crust. They are found in various shapes and sizes and are formed because of extreme geological processes going on in the crust of the Earth. They are majorly classified into three distinct types based on their formation processes and because of which they have their own unique characteristics. The classification of the rocks is as given below:

• Igneous Rocks: These are the types of rocks that are formed because of the solidification of the lava and the magma. This solidification can occur either below the surface or above the surface of the Earth. When it occurs below the surface, they are known as intrusive rocks and they are highly crystalline in feature whereas, when the solidification takes place above the surface, they are known as extrusive rocks and they are highly glassy in feature. Granite is one of the most common examples of igneous rocks in the world and it is an intrusive igneous rock. 

• Sedimentary Rocks: These are the rocks that are formed by the deposition of the fragments of rocks that weathered away due to exogenous processes. Mostly these rocks are formed at the river beds and the fragments are converted into rocks by compaction through a process called lithification. Limestone and silica rock is the most common form of sedimentary rocks found across the world. 

• Metamorphic Rocks: These are the kind of rocks that are formed because of the recrystallisation of the already existing rocks or fragments of rocks. There are various types of metamorphic rocks depending on the layer patterns. Gness is the best example that is found for metamorphic rocks. 

Sedimentary Rocks

As mentioned before the sedimentary rocks are the ones that are formed by the settling of the fragments of rocks that are subjected to different exogenous processes. These fragments are transported because of different processes such as the river flow and then over time are settled whenever suitable conditions are present. These deposits are converted into rocks through compaction in a process called lithification. The sedimentary rocks are classified into the following three major categories depending on their mode of formation:

I. Mechanically Formed: Examples include sandstone, limestone, shale, loess, etc.

II. Organically Formed: Examples include geyserite, chalk, limestone, coal, etc.  

III. Chemically Formed: Chert, limestone, halite, potash, etc. are examples of such types. 

As can be seen, most of the types of rock examples that are formed due to chemical precipitation are the ones that are mostly included in the category of siliceous sedimentary rocks. The siliceous chert is one of the most common forms of such rocks followed by the siliceous limestone which is also one of the pretty common examples of siliceous rocks. Other examples of siliceous sedimentary rocks, also known as silica rocks as these are rocks high in silica, include siliceous dolomite and calc gneiss. Some of the less common forms also include siliceous sandstones in places where they are formed because of certain chemical processes. Of the different types of available silicate mineral rocks, pyroxene rock is also one of them which is nothing but a type of inosilicate i.e. the chain silicates of silicate tetrahedra. 

These siliceous rocks are also not devoid of life. They are known to commonly form the silica-secreting organisms such as the radiolarians, diatoms or other types of sponges. These are one of the salient features of siliceous rocks.