Type Of Rocks

Introduction 

Igneous, sedimentary, and metamorphic rocks are the three types of rocks. The rock cycle includes all of these categories. Changes in circumstances can cause one rock type to transform into another. It could also change into a new form of rock.

A rock is a non-living, naturally formed from the earth material. Collections of mineral grains are kept together in a hard, solid mass to form rocks. What distinguishes a rock from a mineral? Minerals make up rocks. Mineral grains in a rock can be as small as your fingernail or even as large as your finger.

The minerals found in rocks, as well as their texture, are used to identify them. The minerals found in each form of rock are unique. A rock, such as a quartzite, can be made up of grains of only one mineral kind. Rocks are much more commonly made up of a mixture of minerals. The size, shape, and arrangement of mineral grains are referred to as texture.

According to their origination, rocks are divided into three major classes or kinds. Hand samples of rocks that can be transferred from their original position can be analysed. Outcrops, or exposed rock formations that are attached to the ground, can also be investigated at the place where they are found.

There are three types of rocks: 

(1) igneous rocks, which solidify from molten material called magma; 

(2) sedimentary rocks, which are made up of fragments from preexisting rocks or materials precipitated from solutions;

(3) metamorphic rocks, which are made up of igneous or sedimentary rocks that have changed mineralogical composition, texture, and internal structure. Based on different factors, the most important of which are chemical, mineralogical, and textural features, these three classes are further classified into numerous groups and types.

Types of Rocks: General Consideration 

(i) Igneous Rocks

Igneous rocks are formed when magma, a molten mixture of rock-forming minerals and frequently occurring volatiles like gases and steam, solidifies. Igneous rocks are normally created at high temperatures because their constituent minerals crystallise from molten material. They originate from processes deep under the Earth—typically at depths of around 50 to 200 kilometres (30 to 120 miles)—in the mid-to-lower crust or the upper mantle. Intrusive igneous rocks (placed in the crust) and extrusive igneous rocks (extruded onto the surface of the land or ocean bottom), in which case the cooling molten material is known as lava.

Intrusive igneous rocks are crystallized beneath the surface of the Earth, where the gradual cooling permits big crystals to form. Diabase, diorite, gabbro, granite, pegmatite, and peridotite are examples of intrusive igneous rocks.

Extrusive igneous rocks generally come  to the surface and cool rapidly, forming tiny crystals. Some of it cools quickly enough to turn into amorphous glass. Andesite, basalt, dacite, obsidian, pumice, rhyolite, scoria, and tuff are examples of these rocks.

(ii) Sedimentary Rocks 

Sedimentary rocks are those that form at the Earth’s surface and are lithified (compressed and cemented together) with the help of moving water, wind, ice, or living organisms. 

(iii) Metamorphic rocks 

Changes in pre-existing rocks under the influence of high temperature, pressure, and chemically active fluids creates metamorphic rocks. Chemical (compositional) and physical (textural) alterations are possible. 

Rock Cycle 

The rock cycle is a continual process that involves the transformation of existing rocks into new ones. Igneous rocks are primary rocks that give rise to other rocks. Sedimentary and metamorphic rocks can be formed from igneous rocks. Sedimentary rocks are made up of fragments produced from igneous and metamorphic rocks. Metamorphic rocks can be formed from sedimentary and igneous rocks. Subduction allows crustal rocks (igneous, metamorphic, and sedimentary) to be dragged down into the mantle (earth’s interior) and melted into molten magma, which is the source of igneous rocks.

Texture of the rocks 

The size, shape, and arrangement of the grains (for sedimentary rocks) or crystals determine the texture of the rock (for igneous and metamorphic rocks). The degree of isotropy and the extent of homogeneity (i.e., consistency of composition throughout) of the rock is also important. The latter refers to how similar the rock’s bulk structure and composition are in all directions.

The source material of the rock, the conditions and environment of deposition (for sedimentary rock) or crystallisation and recrystallization (for igneous and metamorphic rock, respectively), and subsequent geologic history and change can all be gleaned via texture analysis.

Physical characteristics

Many branches of work, including geology, petrophysics, geophysics, materials science, geochemistry, and geotechnical engineering, are interested in and use the physical properties of rocks. The scale of research extends from molecular and crystalline studies of the Earth and other planetary bodies to terrestrial studies of the Earth and other planetary bodies. Geophysicists study the variation of physical properties of subsurface rocks to detect natural resources such as oil and gas; seismologists formulate prospective earthquake predictions using premonitory physical or chemical changes; crystallographers study the synthesis of minerals with special optical or physical properties; exploration geophysicists study the variation of physical properties of subsurface rocks to detect natural resources such as oil and gas.

Since rocks are made up of mineral grains or crystals, their qualities largely depend upon the properties of the minerals that make them up. The relative qualities and occasionally orientations of the numerous grains or crystals in a rock are averaged to determine these overall properties. As a result, some qualities that are anisotropic on a submicroscopic or crystalline scale are reasonably isotropic for a large bulk volume of the rock. Grain or crystal size, shape, and packing arrangement, the amount and distribution of empty space, the presence of natural cement in sedimentary rocks, temperature and pressure, and the kind and amount of enclosed fluids are all factors that influence many attributes (e.g., water, petroleum, gases). Many rocks have a wide range of these properties, assigning typical values for a property is frequently done using a statistical variation.

Conclusion 

Mineral and chemical composition, permeability, the texture of constituent particles, and particle size etc are all factors used to classify rocks. The processes that created the rocks gave rise to certain physical properties. The rock cycle is a geological concept that describes the transformation of rocks from one kind to another over time. Igneous, sedimentary, and metamorphic rocks are formed as a result of this change.

There are no hard and fast limits between allied rocks, though. They pass through gradations from one to the other by changing the proportions of their minerals; the characteristic structures of one type of rock can therefore be traced, eventually dissolving into those of another.