List the common nonsilicate minerals and explain why each is important.
Nonsilicate minerals are typically divided into groups, based on the negatively charged ion or complex ion that the members have in common. For example, the oxides contain the negative oxygen ions (O22), which bond to one or more kinds of positive ions (Figure 1). Thus, within each mineral group, the basic structure and type of bonding is similar. As a result, the minerals in each group have similar physical properties that are useful in mineral identification.
Although the nonsilicates make up only about 8 percent of Earth’s crust, some minerals, such as gypsum, calcite, and halite, occur as constituents in sedimentary rocks in significant amounts. Furthermore, many others are important economically. Figure 1 lists some of the major nonsilicate mineral groups and gives a few examples of each. Some of the most common nonsilicate minerals belong to one of three classes of minerals: the carbonates (CO3 22), the sulfates (SO4 22), and the halides (Cl12, F12, Br12). The carbonate minerals are much simpler structurally than the silicates. This mineral group is composed of the carbonate ion (CO3 22) and one or more kinds of positive ions. The two most common carbonate minerals are calcite, CaCO3 (calcium carbonate), and dolomite, CaMg(CO3)2 (calcium/magnesium carbonate) (see Figure 1A,B). Calcite and dolomite are usually found together as the primary constituents in the sedimentary rocks limestone and dolostone. When calcite is the dominant mineral, the rock is called limestone, whereas dolostone results from a predominance of dolomite. Limestone has many uses, including as road aggregate, as building stone, and as the main ingredient in Portland cement.
Two other nonsilicate minerals frequently found in sedimentary rocks are halite and gypsum (see Figure 1C,I). Both minerals are commonly found in thick layers that are the last vestiges of ancient seas that have
ong since evaporated (Figure 3.42).
Like limestone, both halite and gypsum are important nonmetallic resources.
Halite is the mineral name for common table salt (NaCl). Gypsum (CaSO4 · 2 H2O), which is calcium sulfate with water bound into the structure, is the mineral from which plaster and other similar building materials are formed.
Most nonsilicate mineral classes contain members prized for their economic value. This includes the oxides, whose members hematite and magnetite are important ores of iron (see Figure 1E,F). Also significant are the sulfides, which are basically com- 3.10 Concept Checks pounds of sulfur (S) and one or more metals. Important sulfide minerals include galena (lead), sphalerite (zinc), and chalcopyrite (copper). In addition, native elements— including gold, silver, and carbon (diamonds)— plus a host of other nonsilicate minerals—fluorite (flux in making steel), corundum (gemstone, abrasive), and uraninite (a uranium source)—are economically important (see GEOgraphics 1 and 2).