Classification of Rocks

Classification of Rocks

Classification of Rocks: The crust of the planet is made up of rocks. The term “rock” refers to a mineral mass that has a more or less homogenous composition. It may be composed of a single mineral (monomineral) or a mixture of minerals (polymineral) (polymineralic). A mineral is a naturally occurring substance that is chemically and physically homogeneous. Minerals are also the result of physical and chemical processes that occur inside the earth’s crust.

Quartz sand, pure gypsum, and magnesite are monomineralized rocks; granite, basalt, and porphyries are polymineralized rocks.

Classification of Rocks
Examples of Rocks

Natural rock materials are commonly employed in construction due to their widespread availability and physical and mechanical characteristics. They are utilized as natural resources, such as gravel and sand, or as machine processed materials, such as crushed stone, sawn, dressed, and polished stones, for a variety of architectural and aesthetic uses.

Rocks are the primary source of mineral binding materials such as gypsum, lime, and cement, as well as artificial rock materials such as brick, glass, concrete, and mortar.

Classification of Rocks

The circumstances surrounding the creation of rocks dictate their chemical and mineralogical makeup, crystalline structure, and texture. These features, which underpin the strength and ornamental features of rocks, serve as the basis for technical and economic evaluations of rocks for use in different construction and installation structures.

The three primary classes are determined by the following criteria:

  • Classification by geological or genetic factors
  • Classification on a physical level
  • Classification on chemical level

Classification on a geological or genetic level

Rocks are classified geologically into three broad categories: igneous, sedimentary, and metamorphic rocks.

Igneous rocks

formed when molten lava cools and hardens. Crystals of various sizes are created depending on the pace of cooling. Large crystals are found in granites, syenites, diorites, and gabbros, while basalts, rhyolites, and andesites contain tiny crystals. In general, igneous rocks are quite hard.

Sedimentary rocks

Transport forces such as wind, water, and ice may transport and deposit loose worn rock elements in the form of sedimentary strata. When exposed to extreme pressure, these sediments undergo compaction and cementation, resulting in sedimentary rocks. Sedimentary rocks include limestone, dolomite, shale, and sandstone.

Metamorphic rocks

formed when sedimentary and, to a lesser degree, igneous rocks experience changes caused by a combination of heat, pressure, and plastic movement (metamorphism). These changes affect the structure, texture, and mineral content of the rocks, resulting in the development of metamorphic rocks. Metamorphic rocks include gneiss, schist, slate, and marble.

Physical Classification

The physical features of rocks, the organization and arrangement of the many particles and mass that comprise a stone, serve as the foundation for this categorization. They are divided into the following categories:

  • Stratified
  • Unstratified
  • Foliated

Stratified Rocks

A stratified structure is generated when a sequence of parallel layers of sedimentary rocks are broken apart. They have different layers that are separable. A cleavage plane is the plane of separation. Stratified rocks include limestone, slate, and sandstone.

Unstratified rocks

They have a granular or crystalline structure and solidify when they cool. They lack stratification, e.g., igneous rocks such as granite and basalt.

Foliated Rocks

These rocks have a distinct parallel arrangement of minerals and a propensity to split in a certain direction, e.g., metamorphic rocks such as gneiss, schist, and so on.

Chemical Classification

Chemical components of rocks determine their categorization. They include the following:

  • Siliceous
  • Argillaceous
  • Calcareous

Siliceous Rocks

Silica is the primary element of these rocks. Silica in its free form is referred to as sand, whereas silica in its mixed form is referred to as a silicate. Silica-bearing rocks in their free state are tougher, but those containing silica in their mixed condition are more prone to dissolve. Sandstone, quartzite, and other silicate rocks are examples.

Argillaceous Rocks

Clay or alumina is the primary element of these rocks. Slate, laterite, and other argillaceous rocks are examples.

Calcareous Rocks

These rocks are mostly composed of calcium carbonate or lime. They are quite susceptible to attack by dilute hydrochloric acid. Examples include limestone and marble.

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