Unit 1: What Are Mineral Resources And What Makes Them Useful?

Unit 1: What Are Mineral Resources and What Makes Them Useful?

Learning outcomes:

1. Define mineral resources.
2. Define a mineral.
3. Give examples of mineral resources and products that contain them.
4. List the most abundant elements in Earth's crust and describe how these relate to the most abundant minerals in the context of resource availability.
5. Summarize the mineral properties that make them useful.
6. Differentiate between rocks and minerals.
7. Name the three main rock families and describe the processes that form them.
8. Infer the relationships between sustainability, resource availability, population growth, and economic development (not covered in reading, but covered in class).

In this reading:

Mineral Resources Minerals Common Elements and Common Minerals Mineral Properties Rocks and the Rock Cycle The Use of Minerals and Rocks in Products Additional Review Questions Glossary

Mineral Resources

In this module, we will consider a mineral resource to be a mineral or rock mined from the earth and used in the products we use daily. Brines (salty waters) are also mined for the elements they contain. These are not minerals but do form via rock-forming processes. Coal, oil, and natural gas are also mined, but these energy resources will be considered separately.

Minerals

Minerals are any substances that meet all of the following criteria:

× Figure 1. Crystalline structure of halite Provenance: Agency: Wikimedia Commons, Image source: http://commons.wikimedia.org/wiki/File:NaCl.png, Accessed August 20, 2014 Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.

1. solid
2. inorganic (or identical to an inorganic mineral). Some minerals, like our teeth, would not be here without our organic processes, but because the apatite (the mineral that makes up our teeth) in our teeth is identical to inorganic apatite, we still consider the apatite of our teeth to be a mineral.
3. natural (or made in a way that mimics nature). Some minerals are made in labs, by people, but because they are made using the same processes that nature uses, we can still consider them minerals. A "synthetic diamond" that is chemically and structurally the same as a natural diamond is still a mineral. However, cubic zirconia, which is made only by people and not by nature, is not a mineral.
4. chemically homogeneous. This means that the mineral contains the same chemicals throughout. Another way to think of this is that you can write one chemical formula that describes the entire mineral (see some examples in the table below). Minerals can contain tiny amounts of impurities. These are elements present in such small quantities that they do not change the mineral's formula but can change the mineral's properties. For example, tiny amounts of impurities can change the color of quartz (a mineral) from clear to pink, or blue, or purple, but the formula remains SiO2.
5. crystalline. This means that the atoms in a mineral are arranged in an orderly and repeating pattern. For example, the chlorine (Cl) and sodium (Na) atoms in the mineral halite are arranged in cubes and these cubes repeat throughout the mineral (see Figure 1 above).

Please note: the "minerals" in a bottle of vitamins and minerals are not real minerals (according to our definition). They are elements that may have been extracted from minerals. This is an example of a word that has a scientific definition that is different from the common-use definition.

Mineral	Chemical formula	Elements in these minerals
quartz	SiO2	Si = silicon, O = oxygen (there are two oxygen atoms for every one silicon atom)
hematite	Fe2O3	Fe = iron, O = oxygen (there are two iron atoms for every three oxygen atoms)
diamond	C	C = carbon
halite	NaCl	Na = sodium, Cl = chlorine (in a 1:1 ratio)

Common Elements and Common Minerals

× Figure 2. Pie graph showing what elements are in Earth's crust (by mass). Provenance: Image by Joy Branlund, Southwestern Illinois College. Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.

Minerals are composed of elements. Eight elements make up the majority of Earth's crust and mantle. As you can see in Figure 2, oxygen (O) is the most common, silicon (Si) the second, and potassium (K), calcium (Ca), sodium (Na), aluminum (Al), iron (Fe), and magnesium (Mg) make up the other six. These elements can combine in a variety of ways to make different minerals. Not surprisingly, most minerals contain silicon and oxygen (plus other elements). These minerals are called silicate minerals. Why do we care about this?

• Sustainability: The eight elements listed above are the most plentiful. Other elements are more rare; we find them less frequently and therefore have a lower overall supply of them.
• Ease of use: Silicate minerals tend to be refractory; they have high melting points and low solubilities, so it is hard to separate the elements within them.
• Although the majority of Earth's elements are found in silicate minerals, they are usually found in higher quantities in nonsilicate minerals, commonly oxide or sulfide minerals. It is more efficient to mine elements when they are found in higher concentrations.
• If mining companies want the element in the mineral (and not the mineral itself), then they seek nonsilicate minerals that contain the element. Even though those minerals are probably less common, it is more efficient (fewer resources are needed) to extract elements from the nonsilicate mineral. For example, the silicate mineral fayalite (Fe2SiO4) contains a lower percentage of iron than does the oxide mineral hematite (Fe2O3), so hematite, not fayalite, is mined for iron.

Mineral Properties

A mineral's chemical and crystalline nature gives it properties that can make it useful. Some of these properties must also be considered when determining how to best mine and process mineral ore and dispose of mine waste. For example:

× Figure 3. Sulfur (S) can be mined from native sulfur (left) or from sulfide minerals such as pyrite (FeS, image on right). Provenance: Photo by Joy Branlund, Southwestern Illinois College. Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.

Chemistry. The elements within minerals give those minerals distinct and useful properties. For example, sulfur allows gunpowder to ignite at a lower temperature and provides fuel for the fire. Aluminum metal is very lightweight but strong. Sulfur can be found as a mineral or as an element within other minerals like pyrite (Figure 3). Aluminum does not form a mineral on its own but must be extracted and concentrated (beneficiated) from the mineral gibbsite.

Hardness. A mineral's hardness is determined by the crystalline nature of that mineral, the type and strength of the bonds that hold the atoms together, and the nature of the repeating pattern. Very hard minerals (such as diamond, corundum, and garnet) are useful as abrasives. For example, sandpaper is often made with garnet sand, and saw blades impregnated with diamonds can cut rock. Talc is used in baby powder because it is a very soft mineral.

Color. Some minerals have distinct and vibrant colors. This makes them incredibly useful as pigments in paints, cosmetics, colored plastic, etc. For example, hematite has a rust-red color and is used in blush and paints (Figure 4). Malachite has a bright green color (Figure 5).

× Figure 5. Malachite's green color has made it useful in paints. Provenance: Photo by Joy Branlund, Southwestern Illinois College. Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license. × Figure 4. The rust color of hematite (left) and the rust-yellow color of limonite (a variety of goethite, right) have long been used for pigments. Provenance: Photo by Joy Branlund, Southwestern Illinois College. Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.

Specific gravity. Specific gravity is a relative density, determined both by a mineral's chemistry (minerals containing more massive elements will have higher specific gravities) and how closely together the atoms are packed.

Behavior of light in the crystal. The crystalline structure determines how light passes through a mineral, or if light is able to pass through a mineral at all. Light reflects inside of diamond, which gives a diamond ring an exquisite sparkle. Other minerals (such as rutile) are quite opaque, which makes titanium oxide (the chemical name of rutile) an important additive in things that need to be opaque, such as paint. Luster describes how light interacts with the surface of a mineral. The mineral hematite can have both metallic or nonmetallic luster; hematite with metallic luster is used to make jewelry. Some minerals are also useful in blocking other wavelengths of light; lead (from the mineral galena) blocks X-rays, for example.

Crystal shape and cleavage are determined by the nature of the crystalline structure. The sheet-like cleavage of muscovite allows it to be broken into tiny pieces of glitter (Figure 6). × Figure 6. Muscovite's cleavage causes it to break into sheets. Provenance: Photo by Joy Branlund, Southwestern Illinois College. Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.

Solubility. Another property of the crystalline structure (the type of bonds) and chemistry causes different minerals to dissolve (turn into the ions that comprise them) differently. Some minerals dissolve quickly in water, whereas others are very stable. The pH of water also affects solubility; some minerals will dissolve faster in acidic water whereas others might dissolve more readily in alkaline waters. For some applications, an insoluble (more stable) mineral is preferred. For example, the Eads Bridge that crosses the Mississippi River is faced with rock made of insoluble minerals below the water line, whereas more decorative limestone (made of the more soluble mineral calcite) faces the support above the water line. Other applications favor soluble minerals. If a mineral is being mined for the element it contains, then it will be easier to extract that element from a soluble mineral.

Magnetism. The chemistry of certain minerals allows them to store an applied magnetic field. For example, magnetic minerals in a computer hard drive can be programmed to store information.

Electric conductivity. The electrical conductivity is mainly determined by the types of chemical bonds; metallic bonds cause metals to have high electrical conductivity, and these are favored for wires (Figure 7). Minerals that have low electric conductivity will be used for insulators, used to block or confine the electric current. × Figure 7. Copper's electrical conductivity and resistance to corrosion make it ideal for electric wiring. Although copper can be found as a pure metal (native copper, upper right), it is often beneficiated from minerals such as chalcopyrite (CuFeS2, lower right).

Thermal conductivity. Minerals can also be used to conduct or confine heat. Thermal conductivity is determined by both a mineral's chemistry and its crystalline structure.

Melting point. Different minerals melt at different temperatures. Minerals with high melting points are used for high-temperature applications. For example, asbestos (several different minerals can make up asbestos) was used in fire-resistant fabrics because of its high melting point.

Behavior in response to stress. Some minerals/rocks are brittle, some are ductile. For example, gold is malleable, which allowed early people to easily shape it into ornaments. An electric current is generated in piezoelectric minerals when a stress is applied. For example, a hammer hits a piezoelectric crystal, and this will generate a spark to ignite a cigarette lighter. The piezoelectricity of quartz allows it to be used to tell time (in quartz crystal watches) and piezoelectricity is also useful in transformers and motors.

Rocks and the Rock Cycle

Rocks are:

1. natural
2. coherent: a rock doesn't fall apart when you pick it up. This means that sand is not a rock.
3. solid

Why is plastic not a mineral?

It is not solid

It is not chemically homogeneous

It is not crystalline

It is not natural

True of false. Plastic is a rock.

True. Plastic is indeed solid and coherent, but is it natural?

False.