3.7: Mineral Groups

Mineral Groups

Most minerals are made up of a cation Links to an external site. (a positively charged ion) or several cations and an anion Links to an external site. (a negatively charged ion). For example, in the mineral hematite (Fe₂O₃), the cation is Fe³⁺ (iron) and the anion is O^2– (oxygen). We group minerals into classes on the basis of their predominant anion or anion group. Groups include the oxides, sulfides, carbonates, silicates, and others. The silicates Links to an external site. are by far the predominant group in terms of their abundance within the crust and mantle. Examples of common minerals from the different groups are given in Table 3.2.

**Table 3.2:** Significant mineral groups and associated examples (CC-BY 4.0, Chloe Branciforte, own work).
Mineral Group	Mineral Examples
Oxides	Hematite, corundum, water ice
Sulfides	Galena, pyrite, chalcopyrite
Sulfates	Gypsum, barite
Halides	Fluorite, halite
Carbonates	Calcite, dolomite
Phosphates	Apatite, Turquoise
Silicates	Quartz, feldspar, olivine
Native Minerals	Gold, diamond, graphite, sulfur, copper

What Do These Mineral Groups Mean?

Oxide Links to an external site. minerals have oxygen (O^2–) as their anion, but they exclude those with oxygen complexes such as carbonate (CO₃^2–), sulfate (SO₄^2–), and silicate (SiO₄^4–). The most important oxides are the iron oxides hematite and magnetite (Fe₂O₃ and Fe₃O₄, respectively). Both of these are important ores of iron. Corundum (Al₂O₃) is an abrasive, but can also be a gemstone in its ruby and sapphire varieties. If the oxygen is also combined with hydrogen to form the hydroxyl anion (OH^–) the mineral is known as an hydroxide. Some important hydroxides are limonite and bauxite, which are ores of iron and aluminum respectively. Frozen water (H₂O) is a mineral (an oxide), but liquid water is not because it doesn’t have a regular lattice.

Sulfides Links to an external site. are minerals with the S^2- anion, and they include galena (PbS), sphalerite (ZnS), chalcopyrite (CuFeS₂), and molybdenite (MoS₂), which are the most important ores of lead, zinc, copper, and molybdenum, respectively. Some other sulfide minerals are pyrite (FeS₂), bornite (Cu₅FeS₄), stibnite (Sb₂S₃), and arsenopyrite (FeAsS).

Sulfates Links to an external site. are minerals with the SO₄^2- anion, and these include anhydrite (CaSO₄) and its cousin gypsum (CaSO₄^.2H₂O) and the sulfates of barium and strontium: barite (BaSO₄) and celestite (SrSO₄). In all of these minerals, the cation has a +2 charge, which balances the –2 charge on the sulfate ion.

The halides Links to an external site. are so named because the anions include the halogen elements chlorine, fluorine, bromine, etc. Examples are halite (NaCl), cryolite (Na₃AlF₆), and fluorite (CaF₂).

The carbonates Links to an external site. include minerals in which the anion is the CO₃^2- complex. The carbonate combines with +2 cations to form minerals such as calcite (CaCO₃), magnesite (MgCO₃), dolomite ((Ca,Mg)CO₃), and siderite (FeCO₃). The copper minerals malachite and azurite are also carbonates.

In phosphate Links to an external site. minerals, the anion is the PO₄^3-complex. An important phosphate mineral is apatite (Ca₅(PO₄)₃(OH)), which is what your teeth are made of.

The all-important silicate Links to an external site. minerals include the elements silicon and oxygen in varying proportions ranging from Si:O₂ to Si:O₄.

Native element minerals Links to an external site. are single-element minerals, such as gold, copper, sulfur, and graphite.