22.4: Nonmetallic Mineral Deposits

Metals are critical for our technological age, but other not-so-shiny materials are also needed to facilitate our way of life. For everything made out of concrete or asphalt, we need sand and gravel. To make the cement that holds concrete together, we also need limestone. For the glass in our computer screens and for glass-sided buildings, we need silica sand plus sodium oxide (Na₂O), sodium carbonate (Na₂CO₃), and calcium oxide (CaO). Potassium is an essential nutrient for farming in many areas, and we also need various types of clay for a wide range of applications (e.g., ceramics and many industrial processes).

Aggregate

The best types of aggregate (sand and gravel) resources are those that have been sorted by streams, and in Canada the most abundant and accessible fluvial deposits are associated with glaciation. That doesn’t include till, because it has too much silt and clay, but it does include glaciofluvial outwash (deposits from glacier-derived rivers), which is present in thick deposits in many parts of the country (Figure 18.15).

Figure 18.15 Sand and gravel in an aggregate pit near Nanaimo, BC. Source: Steven Earle (2015), CC BY 4.0. View source.

In a typical gravel pit, materials are graded on-site according to size. They are then used in a wide range of applications from constructing huge concrete dams to filling children’s sandboxes. Sand is also used to make glass, but for most types of glass, it has to be at least 95% quartz (which the sandy layers shown in Figure 18.15 are definitely not), and for high-purity glass and the silicon wafers used for electronics, the source sand has to be over 98% quartz.

Limestone for Concrete

Approximately 80 million tonnes of concrete are used in Canada each year—a little over 2 tonnes per person. The cement used for concrete is made from approximately 80% calcite (CaCO₃) and 20% clay. This mixture is heated to 1450°C to produce the required calcium silicate compounds (e.g., Ca₂SiO₄). The calcite typically comes from limestone quarries like the one on Texada Island, B.C. (Figure 18.16). Limestone is also used as the source material for many other products that require calcium compounds, including steel and glass, pulp and paper, and plaster products for construction.

Figure 18.16 Triassic Quatsino Formation limestone being quarried on Texada Island, B.C. Source: Steven Earle (2015), CC BY 4.0. View source.

Evaporite Minerals

Evaporite deposits form in restricted basins where water evaporates faster than it recharges, such as the Great Salt Lake in Utah, or the Dead Sea, which borders Israel and Jordan. As the waters evaporate, soluble minerals are concentrated and become supersaturated, at which point they precipitate from the now highly-saline waters. If these conditions persist for long stretches, thick rock salt, rock gypsum, and other mineral deposits accumulate.

Evaporite minerals, such as halite, are used in our food as common table salt. Salt was a vitally important food preservative and economic resource before refrigeration was developed. While still used in food, halite is now mainly mined as a chemical agent, water softener, or road de-icer. Gypsum is a common nonmetallic mineral used as a building material; it is the main component in dry wall. It is also used as a fertilizer. Other evaporites include sylvite—potassium chloride, and bischofite—magnesium chloride, both of which are used in agriculture, medicine, food processing, and other applications. Potash, a group of highly soluble potassium-bearing evaporite minerals, is used as a fertilizer. In hyper-arid locations, even more rare and complex evaporites, like borax, trona, ulexite, and hanksite are mined. They can be found in places such as Searles Dry Lake and Death Valley, California, and in the Green River Formation’s ancient evaporite deposits in Utah and Wyoming.

 

Building Materials

Rocks are quarried or mined for many different uses, such as building facades (Figure 18.17), countertops, stone floors, and headstones. In most of these cases, the favored rock types are granitic rocks, slate, and marble. Quarried rock is also used in some applications where rounded gravel isn’t suitable, such as the ballast (road bed) for railways, where crushed angular rock is needed.

Figure 18.17 Slate used as a facing material on a concrete building column in Vancouver Source: Steven Earle (2015), CC BY 4.0. View source.

Do Know Where to Find the Materials You Need?

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