What is Rock Geology?

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  • Written By: Jason C. Chavis
  • Edited By: Bronwyn Harris
  • Last Modified Date: 17 January 2020
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Rock geology is the science that studies the solid matter of the Earth. It analyzes different physical properties between the various types of rock, what the composition of the rocks are and how the rocks became located in their position. This study is essential to understanding the history of the planet as well as how it formed to its present condition. In industry, rock geology is essential in determining safety in engineering, mitigating the problems associated with building on new surfaces.

The first geologist is believed to be ancient Greek scholar Theophrastus. He published a book, On Stones, in the third century BC. It held its authoritative stances into the early Middle Ages. New concepts about rock geology were introduced by Abu al-Rayhan al-Biruni in the 11th century. He made the case that India was once part of the ocean to explain the varied rock formations and fossils he found. Through his work, he influenced a number of natural philosophers that would ultimately become the principles of geology in the Renaissance.

In 1785, James Hutton introduced the modern theories of rock geology in a paper for the Royal Society of Edinburgh. He formulated a theory that mountains eroded over time and turned into sediments. These sediments then formed into new rocks in the sea and ultimately returned to the dry land. Hutton determined that rocks could inform humanity about the true age of the Earth.


According to rock geologists, rocks are organized into three types: sedimentary, igneous and metamorphic. The type is determined by how the rock originally formed. Igneous rock is crystallized from magma or lava. When this rock is eroded or otherwise weathered it is considered sedimentary rock. Sedimentary rock in turn becomes metamorphic rock when its subjected to intense pressures or heat. All three can be melted once again, starting the cycle over.

Rock geology relies heavily on field work. Since rocks are found in nature, geologists usually need to travel to where the rock deposits are located. Various practices are conducted to map and identify rocks and their structures. Geological mapping allows a geologist to formulate a theory on the full structure and location of different rock formations. This helps determine the level and process of erosion as well as locations of possible archaeological remains. Various methods of identification of the rocks are conducted including seismic tests and physical analysis.

While rock geology in the field is important, lab work is also highly important. Petrologists use two major methods to identify rocks in the lab, both are highly reliable. Researchers use either an electron microprobe or through optical microscopy. The process of using an electron microprobe involves extracting chemical compositions to determine the evolution of rocks. In optical microscopy, thin sections of rock are analyzed using polarized light to identify the different properties of the sample.


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I am an avid rock collector, so I have always been interested in rock geology. I took a class last year, and learned a lot about geology rock samples. The information I got helps me know what to look for when I'm shopping for rocks and minerals, or looking for them in nature.

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