For the InstructorThese student materials complement the Humans' Dependence on Earth's Mineral Resources Instructor Materials. If you would like your students to have access to the student materials, we suggest you either point them at the Student Version which omits the framing pages with information designed for faculty (and this box). Or you can download these pages in several formats that you can include in your course website or local Learning Managment System. Learn more about using, modifying, and sharing InTeGrate teaching materials.
Unit 1: What Are Mineral Resources and What Makes Them Useful?
- Define mineral resources.
- Define a mineral.
- Give examples of mineral resources and products that contain them.
- 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.
- Summarize the mineral properties that make them useful.
- Differentiate between rocks and minerals.
- Name the three main rock families and describe the processes that form them.
- Infer the relationships between sustainability, resource availability, population growth, and economic development (not covered in reading, but covered in class).
In this reading:
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 are any substances that meet all of the following criteria:
- 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.
- 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.
- 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.
- 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
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 PropertiesA 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:
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).
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).×
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
- coherent: a rock doesn't fall apart when you pick it up. This means that sand is not a rock.
Rocks are divided into three groups - igneous, metamorphic, and sedimentary, based on how they formed. On Earth, an existing rock can undergo processes and become a different type of rock, which means that rocks are recycled and the different rock types are all connected according to the rock cycle.
Each rock type will be covered in more detail later. Here are some definitions of terms in the concept map:
magma = liquid rock
weathers = breaks into pieces (called sediments) or sometimes ions (the charged atoms/molecules that made up the mineral)
erodes = pieces are transported (picked up and carried) elsewhere
deposits = pieces are dropped, forming a layer (on a sand dune, or the bottom of a stream, lake, or ocean, for example)
lithifies = sediments harden to become rock (to become coherent)
Later in this module, we will see that the processes in the rock cycle can concentrate mineral resources and turn them into mineral reserves.
The Use of Minerals and Rocks in Products
Sometimes actual minerals and rocks are used in products, or to make things. The rock granite is mined to make countertops, and the mineral halite is mined, crushed, and sold as table salt. Other times, minerals and brines are processed to extract one specific element, and these individual elements are also often called commodities. For example, the commodity aluminum is extracted from the rock bauxite, which contains aluminum-bearing minerals such as gibbsite. The process of extracting the desired mineral or element from an ore is called beneficiation.
The answers listed in the above questions are mineral properties. The reading also discussed the five criteria something needs to meet in order to be a mineral. Come up with a way to clarify the different between the criteria (something needs to meet to be a mineral) and the properties (that might make minerals useful).
Additional Review Questions
Beneficiation: Industrial processes that extract the desired commodity from a rock and/or mineral. Return to text
Cleavage: Describes how a mineral breaks. If cleavage is present, minerals will break cleanly along cleavage planes. Return to text
Commodity: The element, mineral, or rock used to make products. Return to text
Density: The amount of matter in a given amount of space. Can be calculated using mass divided by volume. Return to text
Element: An atom with distinct properties. All known elements are listed on the periodic table. Return to text
Igneous Rock: A rock made when an existing rock melts to make magma, and that magma cools and hardens. Return to text
Metamorphic Rock: A rock made when an existing rock changes due to high temperature, reactive fluids, and/or high pressure. Return to text
Mineral: A substance that is solid, inorganic, natural, chemically homogenous, and crystalline. Return to text
Mineral Resource: Any mineral or rock mined from the earth and used in products. Return to text
Refractory: Relatively unreactive, with low solubility and high melting point. Return to text
Rock: A natural, coherent solid. Return to text
Sedimentary Rock: A rock made when an existing rock weathers to create sediment. The sediment then erodes, deposits, and lithifies to make the sedimentary rock. Return to text
Silicates (silicate minerals): Minerals containing silicon and oxygen (silicate ions). Most minerals are silicates because there is more silicon and oxygen on Earth than any other elements. Return to text
Specific Gravity: Relative density (the density of a rock divided by the density of water). If measured in g/cm3 (grams per cubic centimeter), density and specific gravity are the same, because the density of water is 1 g/cm3. Heavier minerals have higher specific gravities. Return to text