A primary mineral is any mineral formed during the original crystallization of the host igneous primary rock and includes the essential mineral(s) used to classify the rock along with any accessory minerals. In ore deposit geology, hypogene processes occur deep below the earth's surface, and tend to form deposits of primary minerals, as opposed to supergene processes that occur at or near the surface, and tend to form secondary minerals.
The elemental and mineralogical composition of primary rocks is determined by the chemical composition of the volcanic or magmatic flow from which it is formed. Extrusive rocks (such as basalt, rhyolite, andesite and obsidian) and intrusive rocks (such as granite, granodiorite, gabbro and peridotite) contain primary minerals including quartz, feldspar, plagioclase, muscovite, biotite, amphibole, pyroxene and olivine in varying concentrations.
For the classical discussions of the origin of primary ores, see the two publications "Ore Deposits" (1903 and 1913). According to W.A. Tarr (1938) the primary mineral deposits are the result of direct magmatic action; he states that the splitting of magmas results in the basic igneous rocks and their accompanying group of accessory minerals formed by the first crystallization in the magma, on the one hand, and in the acidic igneous rocks and a second group of accessory minerals which were formed by deposition from the residual mother liquors.
Modern soil science offers the following definition: "Primary Minerals: The thickness of the earth's crust varies from 10 km under the ocean to 30 km under the continents. Of the 88 naturally occurring elements on earth, only 8 make [up] most of the crust. The earth's crust and soils are dominated by the silicic acid in combination with Na, Al, K, Ca, Fe and O ions. ...Those elements are components of primary minerals, whereas primary minerals are components of parent rocks. There are almost 3000 known minerals, but only 20 are common and just 10 minerals make up 90 % of the earth's crust. Primary minerals are defined as minerals found in soil but not formed in soil. This definition is different from that of secondary minerals, which are defined as minerals formed in soils." This is further defined by Dr. Broome of North Carolina State:
Two types of minerals are found in natural systems: primary and secondary.
- Whether the mineral is primary or secondary depends on the mode of formation and not on the mineral composition.
- minerals that crystallize from cooling magma are called primary.
- minerals that crystallize during the weathering of primary minerals are called secondary minerals.
Primary rocks are the source of primary minerals and primary water.
- Ailsa Allaby and Michael Allaby. "primary mineral." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 1 Oct. 2016. <http://www.encyclopedia.com>.
- Rakovan, John (2003). "A Word to the Wise: Hypogene & Supergene". Rocks & Minerals. 78 (6): 419. doi:10.1080/00357529.2003.9926759.
- Dept. of Land, Air and Water Resources. University of California Davis. http://lawr.ucdavis.edu/classes/Ssc219/biogeo/prim.htm
- Rickard, T.F.; Ore Deposits: Engineering and Mining Journal, 1903; and Emmons, S.F.; Ore Deposits: A. I. M. E., 1913: pp. 837-846.
- Tarr, W.A.; 1938: Introductory Economic Geology; McGraw-Hill Book Co., Inc., p. 31.
- Grunald, S.; "Primary Mineral Components of Soils"; https://soils.ifas.ufl.edu/faculty/grunwald/teaching/eSoilScience/primary.shtml#parent
- Tarr, W.A.; 1938: Introductory Economic Geology; McGraw-Hill Book Co., Inc.