The following information is adapted from Out of the Rock, which was developed by the National Energy Foundation with funding provided by the United States Bureau of Mines. The following pages provide general mineral resource and mining information in a question-answer format.
What are minerals?
Minerals are naturally occurring solid, inorganic substances made of a regular, repeating arrangement of atoms and molecules. There are 109 types of naturally occurring atoms which are called elements. These elements combine in various ways to make over 3,500 known minerals. However, only twelve elements and fewer than one hundred minerals are relatively abundant. The eight most plentiful elements in decreasing abundance are: oxygen, silicon, aluminum, iron, magnesium, calcium, sodium and potassium. Not surprisingly, the most common minerals are made of oxygen and silicon in combination with the other six abundant elements. Scarce elements, like copper and gold, occur in rarer minerals and are valuable because of their usefulness to society.
Minerals are made of atoms that are arranged in a regular, repeating manner. Compounds that are made in the laboratory are not considered minerals, though they may have the same type and arrangement of atoms found in the naturally occurring material. Minerals are given names on the basis of a particular physical or chemical property (azurite is named for its blue color, hematite - which is red - derives from the Greek word for blood), or they may be named after a locality (minnesotaite from Minnesota; calaverite from Calaveras County, California; franklinite from Franklin, New Jersey), or a person (bornite after von Born, a mineralogist; smithsonite, after the founder of the Smithsonian Institution), or other physical or chemical properties: (Graphite comes from the Greek word meaning to write). Notice that many mineral names end in "ite."
What is the relationship between rocks and minerals?Minerals are considered the buildings blocks of rocks, since most rocks are made of several minerals. Although there are many kinds of rocks, they can be placed in one of three large classes according to the minerals they contain and by their physical features (textures). Igneous rocks form from the magma (melted rock). If the magma cools slowly deep underground, the rock may contain the minerals quartz, feldspar, mica, pyroxene and amphibole. If it cools quickly, such as in a lava flow, the minerals will be microscopic. Some sedimentary rocks form by the accumulation and compaction of sediment carried by rivers. Sandstone is formed by the accumulation of sand-sized particles of quartz and feldspar. Shale contains clay minerals. Limestone is formed by the accumulation of the skeletons of marine organisms. Some sedimentary rocks, such as evaporite deposits containing halite, sylvite, and gypsum, form by direct precipitation from very saline lakes or seas. Metamorphic rocks form when any pre-existing igneous or sedimentary rocks have been deeply buried. Heat and pressure transform the original rocks into metamorphic rocks such as slate, quartzite, schist, and marble. A few rocks are formed of essentially one mineral; e.g., quartzite of quartz. |
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How are minerals grouped?
Minerals are grouped by their chemical composition. The common mineral groups consist of the pure elements, compounds containing metal and oxygen (oxides), compounds containing silicon and oxygen (silicates), compounds containing carbon and oxygen (carbonates), compounds containing metals and sulfur (sulfides), compounds containing sulfur and oxygen (sulfates), and compounds containing fluorine, chlorine or bromine (halides). Minerals can also be grouped by their crystal shapes. There are six basic geometrical ways in which atoms and molecules can be arranged in a crystal. These six arrangements are called the six crystal systems. Minerals belonging to the same crystal system not only have similar outward appearances but also share some physical properties.
What is another, more practical classification system for minerals?
Minerals can also be classified as metallic and nonmetallic and can be further subdivided according to use:
| the term used in the mining industry for minerals that contain iron or other metallic elements which are added to iron to make a variety of steel alloys. The ferrous metals include chromium, cobalt, manganese, molybdenum, nickel, niobium, silicon, titanium, tungsten, vanadium. Many of these elements have other important uses. |
minerals containing other metallic elements seldom if ever alloyed with iron, such as aluminum, copper, gold, lead, mercury, zinc.
The metallic minerals are mined for the purpose of extracting specific metallic elements from them. Very often they occur in mineral associations which make extraction of several elements possible. For example, different types of copper deposits may also contain gold, silver, molybdenum, cobalt, zinc, etc. Copper itself is sometimes a byproduct of nickel mining. |
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| Construction Materials - common rocks and rock materials used chiefly in construction and usually composed of different proportions of the twenty-five most abundant minerals of the earth's crust. These include sand and gravel, crushed stone, and synthetic materials such as cement (from limestone, clay, and gypsum), concrete (from cement and sand or crushed stone), and glass (from silica sand, sodium carbonate, and other minerals). Construction materials are used in enormous amounts. They require minimum processing, and have a relatively low per ton value. Tonnages of these materials are so great that costs of transportation become a very important factor, and urban areas depend heavily on local supplies whenever possible. Other construction materials used in great quantities are clays and dimension stones (marble, slate, granite, or sandstone). |
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minerals used chemically and otherwise in industry because of composition. These include such substances as sulfur, salts, limestone, fertilizers, abrasives, barite, asbestos, industrial diamonds, and refractories.
Industrial materials are much less abundant than construction materials, and deposits are more restricted in distribution and extent. In most cases considerable processing is required to extract the desired substance at the needed purity for the end use. Therefore industrial minerals generally are much more costly than structural materials. |
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From the Ground Up
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