Review: Definition of a Mineral

Minerals are organized according to the anion or anion group (a group of atoms with a net negative charge, e.g., SO₄^2–) they contain, because the anion or anion group has the biggest effect on the properties of the mineral.  Silicates, with the anion group SiO₄^4-, are by far the most abundant group in the crust and mantle. The different mineral groups and some examples of minerals in each group are summarized below.

Oxide Minerals: O^2- Anion

Oxide minerals have oxygen (O^2–) as their anion (see figure below). They don’t include anion groups with other elements, such as the carbonate (CO₃^2–), sulfate (SO₄^2–), and silicate (SiO₄^4–) anion groups. The iron oxides hematite and magnetite are two examples of iron’s important ores. Corundum is an abrasive but can also be a gemstone in its ruby and sapphire varieties. The mineral is known as a hydroxide if the oxygen is combined with hydrogen to form the hydroxyl anion (OH–). Some important hydroxides are limonite, bauxite, and iron and aluminum ores.

Sulfide Minerals: S^2- Anion

Sulfide minerals (Figure below) include galena, sphalerite, chalcopyrite, and molybdenite, which are the most important ores of lead, zinc, copper, and molybdenum, respectively. Some other sulfide minerals are pyrite, bornite, stibnite, and arsenopyrite. Sulfide minerals tend to have a metallic sheen.

Sulfate Minerals: SO₄^2- Anion Group

Many sulfate minerals form when sulfate-bearing water evaporates. A deposit of sulfate minerals may indicate that a lake or sea has dried up at that location.  Sulfates with calcium include anhydrite and gypsum (Figure below). Sulfates with barium and strontium are barite and celestite, respectively. The cation has a +2 charge in all these minerals, which balances the –2 charge on the sulfate ion.

Halide Minerals: Anions from the Halogen Group

The anions in halides are the halogen elements, including chlorine, fluorine, and bromine. Examples of halide minerals are cryolite, fluorite, and halite (Figure below).  Halide minerals are made of ionic bonds. Like the sulfates, some halides also form when mineral-rich water evaporates.

Carbonate Minerals: CO₃^2- Anion Group

The carbonate anion group combines with +2 cations to form minerals such as calcite, magnesite, dolomite, and siderite (Figure below). The copper minerals malachite and azurite are also carbonates.  The carbonate mineral calcite is the main component of rocks formed in ancient seas by organisms such as corals and algae.

Phosphate Minerals: PO₄^3- Anion

The apatite group of phosphate minerals (see Figure below, to the left) includes hydroxyapatite, which makes up the enamel of your teeth. Turquoise is also a phosphate mineral (see Figure below, to the right).

Silicates (SiO₄^4–)

The silicate minerals include the elements silicon and oxygen in varying proportions. These are discussed at length in the next section.

Native Element Minerals

These are minerals made of a single element, such as gold, copper, silver, or sulfur/sulphur (Figure below).

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