Minerals in Geology: Types and Uses

Crystals of augelite and quartz

Minerals are naturally occurring inorganic solid substances. They are the building blocks of rocks. So it is impossible to have a rock without a mineral. Many of the minerals commonly found in rocks include micas, feldspars, and quartz.

These minerals could be made up of one element, or more elements. While it is possible to have single element minerals such as gold and silver, many minerals occur as a combination of several elements. They are crystalline solids

For a substance to qualify as a mineral, it must naturally occur. There are variations to some minerals as many can now be synthesized in the labs. However, no matter how close their resemblances to natural minerals might be, they are not regarded as minerals. All minerals are formed naturally through geologic processes.

The substance that qualifies as a mineral must have a definite internal structure. The internal structure of the mineral describes how the molecules that formed it are arranged. This internal arrangement is peculiar to specific minerals.

It must also be homogeneous. This means it must be made essentially of one material that cannot be separated into other compounds using physical methods. Thus, for those minerals that consist of several elements, these elements or compounds should not be easily separated.

The mineral present in any rock determines the type of rock and its properties. Thus, in igneous rocks such as granites, the most abundant minerals would be feldspars, micas, and quartz. On the other hand for metamorphic rocks, these minerals could be present with the addition of hornblende or garnets.

What is the difference between rocks and minerals?

Rocks and minerals look so much alike. Some rocks could have just one mineral so how do we differentiate a rock and a mineral? The simplest answer: “there are minerals in rocks but no rocks in minerals!”

The easiest way to differentiate between this pair is to understand that a mineral always has the same chemical composition everywhere in the world. For rocks, their composition might vary at different locations.

This could be when there is a slight change in the number of a specific element or mineral. A different mineral or element might also be introduced and so long as it does not alter the defining description, the rock does not change.

The presence of different minerals in rocks at different times allows rocks have varied colors and shapes. For instance, granite could appear white or pink at different times and remain a granite. This is caused by the minerals present at each point. Minerals always have the same composition, shape, and color.

Because minerals have a consistent chemical composition, they can be represented using chemical formulas. The chemical formula for quartz is SiO2, which for calcite is Caco3 while rocks cannot be represented using a chemical formula.

Another difference is that rocks could be made of an aggregate of inorganic and organic materials. Some rocks, especially sedimentary rocks could have organic materials such as coal, lignite, or bitumen as essential parts of the rocks. Meanwhile, minerals are exclusively inorganic substances.

Types of minerals

Minerals are classified based on their chemistry and crystal forms. There are about two broad groups of minerals; silicates and non-silicates. The silicate minerals are those with a basic unit of silica (SiO2) tetrahedron as the foundation. For some minerals formed at extreme pressure conditions, the tetrahedron might be converted to an octahedron. What is important is that the presence of silica.

Non-silicate minerals are minerals that fulfill the conditions required to be named as minerals but have no silicate structures. These are grouped into the Native elements, Oxides, Hydroxides, Sulphides, Sulfates, Carbonates, Phosphates, and Halides.

Native elements

Native Platinum

Native minerals are elements that occur alone. These elements do not chemically bond with another element. The majority of them are found as metals or semi-metals. They exhibit high metallic luster, ductility, and malleability. Depending on their individual characteristics, they can conduct electricity to certain levels. They are among the rarest minerals on earth.

Native minerals can also be sub-divided into groups based on their individual characteristics such as structures and chemical properties.

  • The gold group

Minerals in the gold group are metals such as gold, silver, copper, mercury, aluminum, and lead. Their internal structure is closely packed and similar to that of gold.

  • The platinum group

The platinum-group minerals are known to occur together in the same deposit. This includes platinum, ruthenium, rhodium, palladium, osmium, and iridium. They all occur as transition elements and have similar physical and chemical properties. This group of minerals is well known for its catalytic properties.

  • The iron-nickel group

This group is made of several alloys of iron and nickel. Most of these were deposited on earth by meteorites. Individual members of this group include; iron, nickel, kamacite, taenite, awaruite, and tetrataenite.

Members of this group have similar physical and chemical properties as well. They all have a grey to black appearance and a hardness of 5 on the Moh’s scale of hardness.

  • The arsenic group

Arsenic, bismuth, antimony, and stibarsen are the elements found in the arsenic group of native elements. Minerals in this group are known as metalloids or semi-metals although they have metallic appearances. They all have the triclinic crystal system.

  • The carbon group

Unlike organic carbon formed in association with other elements, native carbon exists as two allotropes. These are diamond and graphite. Graphite as crystalline carbon has its crystals arranged in the hexagonal system. This allows it to be used as a lead in pencil making.

Diamond on the other hand is formed at extreme temperature and pressure. Diamond is known as the hardest mineral on earth and has several industrial uses.

Oxides

Sapphire, a type of corundum. Source: Minerals.net

Minerals in this group arise as a result of the bonding between one or more metals and anion of oxygen (O2-). There are several members of this group. These are stable at standard conditions. This excludes those minerals with silicates.

They are also grouped into simple or multiple oxides depending on the number of metals found in association with oxygen. Minerals with single metals forming oxides such as corundum (Al2O3) are referred to as simple oxides. Multiple oxides arise when there is more than one metal forming the oxide. An example is seen in the case of ilmenite (FeTiO3) and chromite (FeCr2O4).

Further subgroups are identified amongst the oxide mineral groups. There is the corundum group with a 2:3 ratio between the metal and oxygen. This group includes the corundum with two molecules of aluminum to three molecules of oxygen (Al2O3). Hematite (Fe2O3) is also an example of this sub-group.

Minerals with a metal-oxygen ratio of 1:2 belong to the rutile group. Examples here include rutile (TiO2) and cassiterite (SnO2) amongst others.

The physical and chemical properties in this group are varied. This variation includes both very hard members such as corundum and very soft members such as psilomelane.

Other examples are all forms of corundum (ruby, sapphire, hematite, and spinel).

Hydroxides

Geothite. Source: Mindat

When hydrogen and oxygen are added together, they form water. Minerals carrying water molecules (H2O) or hydroxyl (OH) members in their structures are referred to as hydroxide minerals. Hydroxides are formed by the reaction of metals and water molecules, unlike oxides that are formed by just metals and oxygen.

While the hardness of many oxide minerals is high, those of hydroxides are low. They are all formed at lower temperatures through surface processes such as weathering, hydrothermal alterations. Many of these are formed through weathering. The most common examples of hydroxides are magnetite, goethite, and brucite.

Some people group the oxide and hydroxide minerals together.

Sulfides

Galena crystal source: geology.com

Sulfides have the element sulfur in combination with one or two metals. They have similar properties as they often reflect the properties of the metals they bond with. These include metallic luster, high conductivity, and high symmetry in their crystal systems. The hardness of these minerals on the scale of hardness is low.

Many ores containing metals such as iron, zinc, copper, silver, and lead are found as sulfides. The common ore for lead, for instance, is galena (PbS). Pyrite (FeS2O), covellite (CuS), and sphalerite (ZnS).

Other members of this group do not have the element in their structure. Some minerals that have the elements selenium, arsenic, tellurium, and antimony also belong to this group. Their anions in combination with metals are referred to as selenides, arsenides, tellurides, and antimonides respectively.

Sulfates

Gypsum. Source: Geology.com

Sulfates are commonly found in evaporate deposits. They are salts of sulfuric acids (H2SO4).

Minerals within this group have very low hardness with some being very soft. They display varied colors based on the properties of the metal combined with sulfuric acid. The main difference between sulfates and sulfide minerals is the presence of oxygen in the sulfates.

Hydrates of metals such as copper, iron, and zinc are the commonest ways sulfates exist. They can be found as gangue with ores, or as secondary minerals formed during oxidation of sulfide deposits

Common sulfates are baryte (BaSO4), gypsum (CaSO4.2H2O), and Epsom salt (MgSO4. 7H2O)

Carbonates

Calcite; a carbonate mineral. Source: US Geological Survey

The Carbonate group comprises minerals with carbonate ions. This group is also subdivided based on their chemistry and crystal structure.

  • The calcite group:

This group comprises calcite, siderite, etc. Members here have their crystals arranged in the trigonal system.

  • Aragonite Group:

The most famous member of this group is aragonite. This has the same chemical composition as calcite but its crystal structure is in the orthorhombic system.

  • Dolomite Group:

Dolomite group has members that crystalize in the trigonal system. Famous members are dolomite and ankerite.

  • Carbonates with Hydroxide:

Azurite and Malachite are examples of carbonates that contain hydroxyl ions in their chemistry. All the members here crystalize in the monoclinic system.

  • Hydrated Carbonates:

A group of carbonates has water molecules in their chemistry. An example is hydromagnesite.

Phosphates

Monazite, Source: Mindat

For this group, there is a bond between metals, a non-metal, and phosphoric acid [H3 (PO4)]

Based on the way they are formed, there are three groups of phosphates. Some crystallize from the liquid. These are referred to as primary phosphate. An example is apatite [Ca5 (F, Cl, OH) (PO4)3].

Another group is formed through alterations to the primary phosphates. These are known as secondary phosphates. Also, at low temperatures, very fine-grained phosphates are formed from phosphorous-bearing organic materials.

The most common type of phosphates are apatite, monazite, and pitchblende

Halides

Halite crystals. Source: Mineral.net

Minerals in this group contain halogens. Halogens are elements in Group 7 on the Periodic Table. This includes; fluorine, chlorine, iodine, and bromine.

Many of these occur as salts and are readily soluble in water. They are mostly found as deposits from evaporation in arid areas although some occur as rock bodies that can be mined at depths. They often occur with bright colors with each color unique to the halogen present. Many of them have a hardness of about 4 on the hardness scale.

The composition and structure of the halides allow them to be divided into three groups; simple halides, complex halides, and oxyhydroxide-halides. Simple halides are the simplest form of halide occurrences. They are salts formed by the combination of halogen and either alkalis, alkaline earth metals, and transition metals. Examples are halite (NaCl), Fluorite (CaF2), and ammonium chloride (NH4Cl).

Complex halides are formed from tight bonding between halides and specific cations. A common example is cryolite. Oxyhydroxy-halides unlike the other members are insoluble salts. These are rare and are produced through the oxidation of halides containing water. Examples are atacamite, matlockite, and nadorite. The most common member in this group is halite (sodium chloride) used in cooking. Other members are cryolite, fluorite, and sylvite.

Silicates

Epidote Crystals

Silicates are the most common minerals. They are also called rock-forming minerals because they are major compositions of all rocks. Their amount in each rock however could vary. Silicates make up about 90% of the earth’s crust.

They are composed almost entirely of silica (a combination of silicon and oxygen). Silicates can be divided into five major groups depending on their structural arrangement.

  • Orthosilicates:

They are also called neosilicates because of the arrangement between silicon and oxygen.  The structure here is a simple isolated tetrahedral. Examples of orthosilicates are garnet, olivine. When two tetrahedrons are linked together, it forms double tetrahedral (sorosilicate) structures. Epidote is an example of a sorosilicate.

  • Ring silicates.

Ring silicates or cyclosilicates have more than two tetrahedral linked together to form a ring-like system. Some examples are tourmaline, beryl.

  • Chain silicates

Single silicate tetrahedral linked together to form chains. They are also called inosilicates. These chains could be single chains or multi chains as seen in pyroxenes and amphiboles respectively.

  • Sheet silicates

Just as the name, sheet silicates or phyllosilicates are formed from the arrangement of several silicate tetrahedral to form sheets. This is common in minerals like micas, clay minerals.

  • Framework silicates

Framework silicates are also known as tectosilicates. They are a 3D networking of silicate tetrahedral. Examples are quartz, feldspars, and zeolites.

How do these minerals get their names?

Like everything, a name is essential in clearly distinguishing and making identifications. Certainly, with the many minerals we have on earth, it would be very difficult to describe or differentiate each one without a name.

Before 1960, most of the names were given by Greek scientists and were based on several criteria such as what they are composed of, a striking physical property. Some were named based on where they were first discovered, the person that discovered the mineral, or as a tribute to a great scientist. Still, others could be named a famous person or a deity.

The suffix “–ite” often ends the name of most minerals, based on whatever was modified to get the name for such mineral. The Greeks introduced this method and it was coined from the word “lithos” meaning the earth. Some did not have the suffixes but had prefixes like “ine-” or “ide-”.

  • Examples of minerals named based on chemistry or physical property.

  1. Malachite was named by Greeks as “malache” because of its leaf green color.
  2. Azurite named by the Arabs as “azure” meaning blue because of its colo8ur
  3. The name Pyrite means “fire and was given because the mineral could produce a spark when struck with a metal.
  • Examples of minerals named based on where they were first discovered

  1. Labradorite is named after the area “Labrador” in Canada.
  2. Aragonite was first discovered in Aragon, a town in Spain
  3. Brazilianite was named after the country Brazil
  4. Magnetite was also named after the region Magnesia in Greece where it was discovered.
  • Example of minerals named after a person

  1. Covellite is named after the mineralogist Niccolo Covelli who discovered it.
  2. Dumeortierite was named after Eugene Dumortier, a paleontologist.
  3. Goethite after the Johann Wofgang von Goethe
  4. Bridgemanite was named after the physicist Williams Bridgman.
  5. Marie and Pierre Currie have their names immortalized by the radioactive mineral Curite

Some minerals were named after deities such as Neptunite and Aegirine were named after the Roman and Norse gods of the sea respectively.

Today, the study of minerals is known as mineralogy, and people trained to study them are referred to as mineralogists. These people have the duty of doing the naming. Many mineralogists belong to an association that controls or oversees all that concerns mineralogy. This is known as the International Mineralogical Association.

Uses of minerals

Nutrition and Health

  • Some minerals are essential components of the body, food and perform vital functions in the body. Minerals like zinc are important for boosting the body’s immunity. Calcium is also important for growing healthy teeth and bones. Iron also plays an important role in helping oxygen move around the body.
  • Common salt is an essential ingredient in cooking as seasonings and in food preservation. It is mined as halite (sodium chloride).
  • Many body care products contain essential minerals such as potassium and fluorine used in toothpaste.
  • Some elements such as radioactive iron and iodine are used as tracers to monitor conditions such as anemia and goiter.

Industrial uses

  • Those that have metallic elements such as copper and aluminum are important in the manufacturing of electrical materials due to their conductive materials. Silver as a metal has the highest conduction but is not a popular choice because it is expensive.
  • Some metals such as gold, zinc, and tin are used in electroplating other metals. This is a method of preserving metals from rust or corrosion.
  • Gold and silicone are essential elements used in making electronics such as computers.
  • Diamond due to its hardness and resistance to abrasion is an important abrasive in many industries. It is also used in making drill bits for some drilling machines.
  • Some domestic items such as cutleries are made of stainless steel which is an alloy of iron. Aluminum is also used for making cooking utensils because of its heat conduction abilities.
  • Salts of some elements such as beryllium are used in fluorescent lamps, x-ray tubes and
  • Insulators in many electrical systems are made from feldspars.
  • Strong alloys of beryllium are used in the aircraft industry.
  • Radioactive minerals such as uranium are used in nuclear energy generation.
  • Quartz is used in making glass. It is also used to make precision instruments and abrasives because of its hardness.
  • Some materials such as halite and potash are used for decorations on ceramic works and brass respectively.

Construction

  • Many metals are used in buildings, manufacturing, and construction. A good example is an iron which is can be used to make rods and bars in buildings.
  • Feldspars can be mined in large quantities and used in making tiles, ceramics, and roofing materials.
  • Manganese is also combined with iron to produce strong alloys that are used in construction projects.

Other Uses

  • Minerals with high reflective properties such as gold, emerald, and sapphire are used as gems in making pieces of jewelry.
  • Potassium, nitrogen, and phosphate rocks are important ingredients in making fertilizers and as additives to livestock feeds
  • Gold, silver, and nickel are also used in making coins
  • Pencil leads are made out of graphite.
  • Micas are used as additives in several manufacturing processes like making plastics, paints, and rubber.

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