Mineral Resources: Why bother?

Mineral resources

Mineral resources are:

• minerals or rocks mined from the earth and used in the products we use daily.

• Coal, oil and natural gas are also mined, but these energy resources will be considered separately.

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 counter tops, 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 often called mineral commodities. For example, the commodity aluminum is extracted from the rock bauxite, which contains aluminum-bearing minerals like gibbsite.

• The process of extracting the desired mineral or element from an ore is called beneficiation.

Minerals

Minerals are:• solid

• inorganic (or identical to an inorganic mineral)

• natural (or made in a way that mimics nature)

• chemically homogeneous – (the mineral contains the same chemicals throughout)

• crystalline (the atoms in a mineral are arranged in an orderly and repeating pattern)

Mineral Quartz Hematite Diamond Halite

Chemical formula

SiO2 Fe2O3 C NaCl

Elements in these minerals

Si = silicon, O = oxygen (two oxygen atoms for every one silicon atom)

Fe = iron, O = oxygen (two iron atoms for every three oxygen atoms)

C = carbon Na = sodium, Cl = chlorine

Crystal structures

 

Si O Fe O C

Na Cl

Crystal structure models from: http://webmineral.com

Examples of minerals

The "minerals" in these “vitamins and minerals” are not real minerals. These are elements that may have been extracted from minerals.

NOT minerals

• Minerals are comprised of elements.

• Eight elements make up the majority of Earth's crust and mantle:

Elements in the crust Mass%

Oxygen (o) 46.6%

Silicon (Si) 27.72%

Aluminum (Al) 8.13%

Iron (Fe) 5.00%

Calcium (Ca) 3.63%

Sodium (Na) 2.83%

Potassium (K) 2.59%

Magnesium (Mg) 2.09%

What’s within the crust (by mass)

Oxygen

Silicon

Common metals (Al,Fe,Ca,

Na, K, Mg)

All others

Common elements and common minerals

• These elements can combine in a variety of ways to make different minerals.

• Most minerals contain silicon and oxygen (plus other elements). These minerals are called silicate minerals.

Common elements and common minerals

FeAlSiO

Crystal structure of almandine garnet (Fe3 Al2 Si3 O12 )

containing iron and aluminum in addition to silicon and oxygen.

Crystal structure of almandine garnet (Fe3 Al2 Si3 O12 )

containing iron and aluminum in addition to silicon and oxygen.

Why do we care about this?• Sustainability: The eight elements just listed are the most

plentiful. Other elements are more rare; we find them less frequently and 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 they hold onto the elements within them.

• If we want the element in the mineral (and not the mineral itself), then we seek non-silicate minerals that contain the element, because it is easier (fewer resources are needed) to extract those elements from the mineral.

Common elements and common minerals

For example, the silicate mineral fayalite (Fe2SiO4) contains iron (Fe). However, it has a melting point of 1205oC, and so it will take a lot of energy if we want to extract iron from fayalite. It is easier to extract iron from hematite (Fe2O3), which is a non-silicate mineral.

Fayalite. Not an economic source for iron, though they contain iron

Hematite. Iron is commonly extracted from this mineral.

Mineral properties

• A mineral's chemical and crystalline nature gives them properties that make them useful.

• These properties also must be considered when determining how to best mine, process, and dispose of the mineral and mine waste.

• The elements within minerals give them distinct and useful properties.

Mineral properties: Chemistry

For example: – sulfur allows gunpowder to ignite at a

lower temperature, and provides fuel for the fire.

Sulfur can be found as a mineral (native sulfur,

S)

Sulfur can be found as a mineral (native sulfur,

S)

Sulfur can also exist as an element within other minerals like pyrite (FeS).

Sulfur can also exist as an element within other minerals like pyrite (FeS).

For example: – Aluminum metal is very

lightweight but strong.

Aluminum alloys were extensively used for constructing Apollo 16

whose Command and Service Module (CSM) "Casper" is shown here

Aluminum alloys were extensively used for constructing Apollo 16

whose Command and Service Module (CSM) "Casper" is shown here

Photo from NASA (http://grin.hq.nasa.gov/ABSTRACTS/GPN-2002-000069.html

Aluminum does not form a mineral on its own, but is beneficiated from the minerals

gibbsite and bohemite.

Aluminum does not form a mineral on its own, but is beneficiated from the minerals

gibbsite and bohemite.

Mineral properties: Chemistry

A mineral's hardness is determined by:

– The crystalline nature of that mineral,

– The type and strength of bonds that hold the atoms together, and,

– The nature of the repeating pattern

CarbonCarbon

Crystal structure for graphite

Crystal structure for graphite

Crystal structure for diamond

Crystal structure for diamond

Both graphite and diamond are made up of the same element, carbon (C). However, diamond is much harder than graphite.

Crystal structure models from: http://webmineral.com

Mineral properties: Hardness

For example:Very hard minerals (like diamond, corundum, and garnet) are

useful as abrasives. Saw blades impregnated with diamonds can cut rock, and sandpaper is often made with garnet sand.

Mineral properties: Hardness

Talc (hardness=1 on the Moh’s scale of hardness) is used in baby powder because it is a very soft mineral.

Almandine garnet crystals. Hardness of almandine garnet is 7-8

On the Moh’s scale of hardness

Almandine garnet crystals. Hardness of almandine garnet is 7-8

On the Moh’s scale of hardness

Some minerals have distinct, and vibrant, colors. This makes them incredibly useful as pigments in paints, cosmetics, colored plastic, etc.

The rust red color of hematite (left) and rust yellow color of goethite (right) have long been used as a pigment.

Malachite’s green color has made it useful in paints

Mineral properties: Color

For example: The native people in Himba Village, Namibia, powder iron oxide minerals (like hematite and goethite) to color their skin and hair. Photo by Ansu John

Mineral properties: Color

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

Mineral properties: Specific gravity

Galena (PbS) contains the heavy element lead, giving it a high specific gravity

The crystalline structure determines if and how light passes through a mineral. For example, light reflects inside of diamond, which gives diamond ring an exquisite sparkle.

Other minerals (like rutile) are quite opaque, which makes titanium oxide (the chemical name of rutile) an important additive in things that need to be opaque, like paint.

Some minerals are also useful in blocking other wavelengths of light; barite and lead (from the mineral galena) block X-rays, for example.

The crystalline structure of calcite (Iceland spar variety) can split light rays passing through it, making the horizontal lines seen through the calcite crystal appear to double up in this photo. Iceland Spar crystals are used in polarizing microscopes and telescopes because of this property.

Mineral properties: Behavior of light in the crystal

Luster describes how light interacts with the surface of a mineral.

For example, the mineral hematite can have both metallic or nonmetallic luster; hematite with metallic luster (photo on left) is used to make jewelry.

Mineral properties: Luster

http://www1.macys.com/index.ognc?cm_sp=navigation-_-top_nav-_-macys_icon

These 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.

Muscovite’s cleavage causes it to break into sheets.

Mineral properties: Crystal shape and cleavage

Different minerals dissolve differently depending on their crystalline structure (the type of bonds) and chemistry. When a mineral dissolves, it breaks into the ions that it contains.

Some dissolve quickly in water (or acidic or alkali solutions), whereas others are very stable.

Mineral properties: Solubility

For example, people eat tablets made of calcite; that calcite dissolves in the stomach, neutralizing some of the acid and reducing heartburn

TUMS® tablet dissolving in acidic water releasing bubbles of carbon dioxide.

TUMS® tablet dissolving in acidic water releasing bubbles of carbon dioxide.

For some applications, an insoluble 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.

If a mineral is being mined from the element it contains, then it will be easier to extract that element from a soluble mineral.

Mineral properties: Solubility

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

A bar magnet hanging from a sample of magnetite. Magnetite is an iron oxide (Fe3O4), and is naturally magnetic.

Mineral properties: Magnetism

Electrical conductivity is mainly determined by the presence of metallic bonds. Metals have these bonds, which is why metals are favored for wires.

Copper is often beneficiated from minerals like chalcopyrite (CuFeS2).

Copper’s electrical conductivity and resistance to corrosion make it ideal for electric wiring.

Copper can be found as a pure metal (native copper, Cu)

Mineral properties: Electrical conductivity

Minerals that have low electric conductivity will be used for insulators, which block and/or confine the electric current.

Mineral properties: Electrical conductivity

Ceramic insulators made from clay minerals are used for supporting electric power lines

Clay minerals such as kaolinite show very low electrical and thermal

conductivity.

Image: FreeD

igitalPhotos.net

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

Mineral properties: Thermal conductivity

Ceramic kitchen utensils made from clay minerals are used to confine the temperature of food and beverages

Clay minerals such as kaolinite show very low electrical and thermal

conductivity.

Different minerals melt at different temperatures. Minerals with high melting points are used for high temperature applications.

For example, the mineral graphite is used for lining furnaces and as crucibles for melting metals

Mineral properties: Melting point

Piezoelectricity is another property related to stress. 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.

Mineral properties: Response to stress

Different minerals/rocks behave differently under stress. For example, while many minerals will shatter if hit with a hammer, gold is malleable. This allowed early people to easily shape it into ornaments.