Contents
Page topics: Native element minerals; halides; oxides; sulfides; sulfates; carbonates
Image above: A variety of non-silicate minerals (clockwise from top left: fluorite, blue calcite, hematite, halite (salt), aragonite, gypsum). Image created by Jonathan R. Hendricks for PRI's Earth@Home project (CC BY-NC-SA 4.0 license).
Overview
There are many different groups of minerals, all organized based on their underlying chemistry and atomic structure. Silicate minerals—those featuring silica tetrahedra—were covered on the previous page. This page introduces some of the most important groups of non-silicate minerals. It is important to note that there are additional mineral groups beyond those covered below.
Native Element Minerals
Native element minerals are composed of a single element, resulting in very simple chemical formulas! Examples include gold (Au), silver (Ag), platinum (Pt), sulfur (S), copper (Cu), and iron (Fe). Diamond and graphite are also native element minerals, both composed entirely of carbon. The ways in which the carbon atoms are bonded dictates their very different properties. In diamond, the carbon atoms are densely packed into a tetrahedral framework (each carbon atom is covalently bonded to four others). In contrast, the carbon atoms that make up graphite are arranged in sheets that have very weak bonds between them. These differences in atom structure cause diamonds to be the hardest minerals, while graphite is so soft that it is used within pencils for writing (pencil "lead" has always been composed of graphite).
Comparison of the atomic structures of diamond and graphite, both of which are composed entirely of carbon. Model by "Dominicm99" (Sketchfab).
Halides
Halides are minerals that are typically composed of cations with +1 or +2 charges (e.g., sodium (Na) or calcium (Ca)) ionically bonded to anions in the halogen group on the periodic table (group 7A), which includes fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). The most familiar example of a halide mineral is halite (NaCl), better known as table salt. Its highly symmetrical atomic structure is demonstrated by the model below, and is also reflected at the hand-sample scale by salt's distinctive cubic cleavage.
Atomic structure of halite (table salt), a type of halide mineral. The larger yellow spheres represent chlorine (Cl) and the smaller green spheres represent sodium (Na). Model by Earth Sciences, University of Newcastle (Sketchfab).
Example: Halite
Formula: NaCl
Properties: Cubic cleavage; transparent; salty
Abundant in this rock: Halite deposits
Halite (NaCl), or table salt, is a mineral in the halide group. This specimen is from the teaching collections of the Paleontological Research Institution. Longest dimension is 5.5 cm.
Example: Fluorite
Formula: CaF₂
Properties: Cubic crystals with octahedral cleavage; color highly variable; luster vitreous.
Abundant in these rocks: Hydrothermal veins, in carbonate vugs
Fluorite (CaF₂) is a mineral in the halide group. This specimen is from the teaching collections of the Paleontological Research Institution. Longest dimension is 5 cm.
Oxides
Oxide minerals are characterized by metal cations (e.g., iron and aluminum) that are usually ionically bonded to oxide (O²⁻) anions. This group of minerals is economically important because they are a major source of metals used in industry. For example, hematite is a major source of iron that is used to produce steel. Magnetite is another example of an oxide mineral.
Example: Hematite
Formula: Fe₂O₃
Properties: Reddish-brown to black; luster metallic
Abundant in these rocks: Banded iron formations and many other types of sedimentary and metamorphic rocks.
Trivia: Hematite is the most important source mineral for iron that is used to manufacture steel.
Sulfides
As their name suggests, sulfide minerals contain sulfur anions (S²⁻). These anions are bonded to metal cations such as iron (e.g., pyrite, FeS₂), lead (e.g., galena, PbS), and mercury (e.g., cinnabar, HgS). Rocks containing sulfide minerals are important sources of metals that are used in industry.
Example: Pyrite (Fool's Gold)
Formula: FeS₂
Properties: Color golden, luster metallic, opaque, crystals sometimes cube-shaped with striations
Abundant in these rocks: Common in metamorphic and sedimentary rocks.
Trivia: Some fossil invertebrates are preserved as pyrite, a result of mineral replacement (example of a pyritized brachiopod).
Sample of the mineral pyrite, a type of sulfide. Model by Earth Sciences, University of Newcastle (Sketchfab).
Example: Galena
Formula: PbS
Properties: Gray color, luster metallic, cubic cleavage
Abundant in these rocks: Found in many types of sedimentary and metamorphic rocks.
Trivia: Galena provides the world's major source of lead; lead is poisonous and is used less now in industry than it was in the past.
Sample of the mineral galena, a type of sulfide. Model by Nate Siddle and the University of Queensland School of Earth Science (Sketchfab).
Sulfates
Sulfate minerals are characterized by a sulfate anion ([SO₄)²⁻]) composed of one sulfur atom bonded to four oxygens. The sulfate anion in turn is bonded to cations in sulfate minerals. The most important sulfate mineral is gypsum (CaSO₄⋅H₂O), which is used in plaster and drywall. As indicated by its chemical formula, gypsum contains water molecules that are bonded to both the sulfate anion and calcium cation. Gypsum forms an evaporitic sedimentary rock of the same name. Barite and anhydrite are other examples of sulfate minerals; unlike gypsum, they lack water molecules.
Example: Gypsum
Formula: CaSO₄⋅H₂O
Properties: Typically colorless, white, or gray; luster vitreous; transparent to translucent
Abundant in this rock: Found in evaporitic sedimentary rocks.
Trivia: Drywall is derived from gypsum, making it an incredibly important mineral for building construction.
Sample of the sulfate mineral gypsum from the teaching collections of the Paleontological Research Institution. Longest dimension of specimen is 8 cm (Sketchfab).
Carbonates
All carbonate minerals possess cabonate anions ([CO₃]²⁻) composed of single carbon atoms that are bonded to three oxygen atoms in a triangular shape. These carbonate anions form sheets linked by cations such as calcium (Ca²⁺) or magnesium (Mg²⁺).
Atomic structures of the carbonate minerals calcite, aragonite, spherocobaltite, and vaterite. Carbon atoms are colored black, oxygen atoms are colored red, and cations are colored either blue (calcium) or purple (cobalt). Model by "fecr2o4" (Sketchfab).
Examples of carbonate minerals include calcite (CaCO₃), aragonite (CaCO₃), and dolomite CaMg(CO₃)₂. Note that calcite and aragonite have the same chemical formula. They are polymorphs of CaCO₃, meaning that they have the same chemical formula, but very different atomic structures. (Graphite and diamond, both composed entirely of carbon, are also examples of polymorphs; see above.) Many marine organisms, for example foraminifera, corals, mollusks, and brachiopods, make their skeletons or shells out of either calcite or aragonite. Calcite and dolomite are the major mineral constituents, respectively, of the carbonate sedimentary rocks limestone and dolostone.
Example: Calcite
Formula: CaCO₃
Properties: Typically white or colorless, but many colors are possible (including blue); rhombohedral cleavage; colorless, transparent specimens exhibit double refraction
Abundant in this rock: Limestone
Trivia: Many organisms construct their skeletons or shells out of calcite
Sample of calcite, a carbonate mineral. Model by Nate Siddle and the University of Queensland School of Earth and Environmental Sciences (Sketchfab).
Example: Aragonite
Formula: CaCO₃
Properties: Colorless, white, or other colors; luster vitreous
Trivia: Many mollusks and corals make their shells or skeletons out of aragonite. Aragonite is less stable than calcite, however, so aragonitic species are sometimes represented in the fossil record only by internal and external molds.
Sample of the carbonate mineral aragonite (CaCO₃). Specimen is from the teaching collections of the Paleontological Research Institution. Longest dimension of specimen is approximately 8.5 cm.
References and Further Reading
Klein, C., and C. S. Hurlbut, Jr. 1999. Manual of Mineralogy, after J.D. Dana. John Wiley & Sons, Inc., New York, 681 pp.
Press, F., and R. Siever. 1994. Understanding Earth. W. H. Freeman and Company, New York, 593 pp.