LITHOLOGY: HISTORY, WHAT IT STUDIES, TYPES - GEOGRAPHY - 2025

The lithology is a branch of geology that is responsible for studying the characteristics of the various types of rocks that exist on Earth. The term comes from the Latin: litho (rock) + logia (study of). Lithology does not study deep features of rocks in general, but rather focuses on the surface features of the rocks.

That is, this discipline studies the color, size, texture and composition of rocks. It stands out and differs from other similar branches of geology, such as petrology, because it studies rock formations without making use of visual zoom tools, such as microscopes.

Vertically inclined metamorphic rocks near Carn Eighe in the Northern Highlands of Scotland.

This is a long-standing discipline, since the first approach to lithology was in 1716. Through this type of study, it was possible to begin to categorize the different rocks that exist, to understand their particularities and their functionalities.

Among its various uses, lithology stands out as one of the main branches of science used in the creation of geological maps. The use of lithology can have various purposes; however, it is also common to use this geological branch in geophysical studies when combined with mathematical formulas.

History

Lithology is a branch of geology whose origin dates back to 1716. Throughout its existence, the evolution of this science has given rise to various types of studies related to rock formations, mountains, the soil and the earth's subsoil.

Therefore, the concept of lithology was created to encompass all studies related to the observation and description of the characteristics of rocks on the Earth's surface.

Unlike other branches of geology, lithology focuses on studying rocky outcrops primarily. This refers to places on the earth's surface where it is possible to see concentrations of rock that has risen from the subsoil of the planet, as an effect of time or seismic movements.

However, the concept can also refer to the study of samples of any type of rock and its characteristics. Lithology is also responsible for studying rock formations present below the surface of the Earth, or even rocks present on the surface expelled by magma eruptions.

What does lithology study?

Lithology categorizes rocks and names them according to their different attributes. However, before defining what type of studies lithology performs, it is important to know the three main types of rock.

Sedimentary rocks

They are all those that are formed by the accumulation of the worn remains of other rocks, known as clastic sedimentary rocks. They can also be formed by the accumulation of sediments and their consolidation in the form of new rocks.

Likewise, it is common for them to be formed by biogenic processes related to secretions or other activities of animals or plants, and by the natural precipitation of liquids.

Igneous rocks

They are formed after the solidification of molten rock or magma. In turn, they are subdivided into two types of rocks: intrusive igneous rocks, which solidify below the surface of the Earth; and extrusive igneous rocks, which form on the surface after an eruption of magma in the subsoil.

Metamorphic rocks

They are rocks that are found below the earth's surface, but that have been structurally affected and modified by heat, humidity or chemical processes. This exposure alters its own chemical composition, texture, and mineralogy.

In lithological studies, the type of rock to which each object of study belongs is taken into account to determine its origin.

Once the type of rock has been determined, it seeks to study other elements in more depth, such as the size of the grains that make it up, its texture, minerals, color and structure. Based on this, a name is determined and a category is assigned for each type of rock.

Types of lithology

The name of the lithology of a rock is determined by the category to which it belongs, determined in turn by a lithological study.

Categorization of rocks

The three main types of rocks, according to lithology, are named according to these principles:

- Sedimentary

Sedimentary rocks are categorized according to the origin of their structure: carbonate or siliciclastic.

In turn, the subcategories of the rocks formed by these elements are also considered as sedimentary rocks for all lithological naming.

- Igneous

The naming and categorization of an igneous rock is made after determining the size of its crystals and its mineralogy.

- Metamorphic

Metamorphic rocks can be named by their various characteristics: texture, protolith, metamorphic facie, or the place where they were found.

These characteristics are determined by the same lithological study, which commonly also gives rise to the name of the rock.

Size of your grains

In studies of igneous and metamorphic rocks, the size of the crystals present in the rock is usually used as the basis for their categorization.

In igneous rocks, this helps to identify the cooling process and how the rock did it: if the rock has large crystals, it is likely an intrusive rock, whereas if it has small crystals, it is usually identified as extrusive.

Mineralogical composition

In all rocks whose mineral grains can be identified using a manual magnifying lens, it is common to include in the description the mineralogy that can be seen in the study.

The mineral composition of the rocks is one of the main parameters used in lithological studies for their categorization.

Color

Many rocks have distinctive colors that must be categorized at the time of a lithological study. In fact, a particular color table is often used for categorizing terrestrial elements, based on the Munsell Color System.

This system was created in the early 20th century and adopted in the mid-1930s as the official palette for terrestrial studies.

Structure

The structure of a rock serves to describe the configuration of all the elements that compose it.

This configuration is generated at the time of the formation of each rock. Sedimentary, metamorphic, and igneous rocks have a different structure, which helps to identify and categorize them more easily.

Texture

The texture of a rock is what describes its relationship with the individual grains present in it or with the clasts that make it up.

In sedimentary rocks the classification and shape of the clasts is taken into account, in metamorphic rocks the growth time of each mineral is taken into account, and in igneous rocks the size of their mineral grains is usually considered.

References

1. Etymology of Lithology, (nd), 2018. Taken from etymonline.com
2. Sedimentary Rock, (nd), 2018. Taken from sciencedaily.com
3. Whitcombe, DN, Connolly, PA, Reagan, RL, & Redshaw, TC (2002). Extended elastic impedance for fluid and lithology prediction. Geophysics, 67 (1), 63-67.
4. Sedimentary Rocks, Hobart M. King, (nd). Retrieved from geology.com
5. Igneous Rocks, Hobart M. King, (nd). Retrieved from geology.com
6. Metamorphic Rocks, Hobart M. King, (nd). Retrieved from geology.com
7. Munsell Color System, (nd), February 8, 2018. Taken from Wikipedia.com
8. Lithology (nd), September 3, 2017. Taken from Wikipedia.com