Primary rock is an early term in

geology Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ear ...

that refers to

crystalline rock A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macrosc ...

formed first in geologic time, containing no organic remains, such as

granite Granite () is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies undergro ...

gneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures an ...

and

schist Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes o ...

as well as

igneous Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...

and

magmatic Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...

formations from all ages. Webster's Revised Unabridged Dictionary published in 1913 provides the following term as used in geology: Ninety years later the McGraw-Hill Dictionary of Scientific & Technical Terms published in 2003 places the term in the geologic field of

petrology Petrology () is the branch of geology that studies rocks and the conditions under which they form. Petrology has three subdivisions: igneous, metamorphic, and sedimentary petrology. Igneous and metamorphic petrology are commonly taught together ...

: The term dates from the late 18th century (see Giovanni Arduino and

Abraham Gottlob Werner Abraham Gottlob Werner (; 25 September 174930 June 1817) was a German geologist who set out an early theory about the stratification of the Earth's crust and propounded a history of the Earth that came to be known as Neptunism. While most tenet ...

) when the first attempts to formulate a

geologic time scale The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochrono ...

divided crustal rocks into four types: Primary, Secondary,

Tertiary Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...

, and

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...

. Darwin used the phrase "primary rocks" in 1838 in the Geological Introduction to Zoology of The Voyage of HMS Beagle Fossil Mammalia Described by Richard Owen The last two terms have survived on most geological time scales used in the 20th and 21st centuries. For an example of the extensive use and explication of this term as debated in the mid-18th century, see "On the Origin of Eruptive and Primary Rocks" by Thomas Macfarlane and published in three parts in The Canadian Naturalist and Geologist Journal of 1863. And for an example in Australian geology literature, where it is capitalized to stress the unique use of the word, see "Report on Country in the Neighborhood of Lake Eyre" by H.Y.L. Brown, Government Geologist, published in 1892. Primary rock is also referred to as primitive rock,

pluton In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

ic rock, and the crystalline

basement A basement or cellar is one or more floors of a building that are completely or partly below the ground floor. It generally is used as a utility space for a building, where such items as the furnace, water heater, breaker panel or fuse box, ...

rock of the Earth's continental

craton A craton (, , or ; from grc-gre, κράτος "strength") is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging and ...

s. It is also loosely, and less precisely, referred to as

bedrock In geology, bedrock is solid Rock (geology), rock that lies under loose material (regolith) within the crust (geology), crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface mater ...

, especially in civil engineering, geophysical surveys and drilling science. The Austrian-American astrophysicist Thomas Gold utilized this term in his book "The Deep Hot Biosphere"Gold, Thomas; The Deep Hot Biosphere; Springer Verlag New York Inc. (1999): p. 107. in the chapter titled "The Siljan Experiment" regarding the deep drilling project in Sweden to prove the theory of abiotic/abiogenic oil and gas: "...the ground of Sweden, composed almost entirely of primary rock and not of sediments...."

References

{{reflist Geology terminology