What are minerals - You use objects that are made from minerals every day, even if you do not realize it. You are actually eating a mineral when you eat food that contains salt. You are drinking from a container made from a mineral when you drink from a glass. You might even wear silver jewelry. The shiny metal silver, the white grains of salt, and clear glass may not seem to have much in common, but they are all made from minerals.
Silver is a mineral. Table salt is the mineral halite. Glass is produced from the mineral quartz. Scientists have identified more than 4,000 minerals in Earth’s crust. Some minerals are found in very large amounts, but most minerals are found in small amounts. If minerals can be so different from each other, what makes a mineral a mineral?
A mineral is a crystalline solid formed through natural processes. A mineral can be an element or a compound, but it has a specific chemical composition and physical properties that are different from those of other minerals. Silver, tungsten, halite, and quartz are all examples of minerals. Each one has a different chemical composition, as well as different physical properties such as crystalline structure, hardness, density, flammability, and color. For example, silver is shiny and salt is white.
Natural Processes
Minerals are made by natural processes. A natural process occurs in or on the Earth. One common natural process that forms minerals is the crystallization of magma. Some natural processes shape Earth’s features, while others include volcanic activity and the movement of tectonic plates. Rocks and minerals are formed in sedimentary layers of sand and mud and in the folding of those layers deep in the Earth, where they are exposed to high pressures and temperatures. A technician might make a gemstone in the laboratory, but this would have been created synthetically, not by natural processes.
Inorganic Substances
A mineral is an inorganic substance, which usually means it was not made by living organisms. Organic substances are all the carbon-based compounds made by living creatures, including proteins, carbohydrates, and oils. This definition includes fossil fuels such as coal and oil, which were originally made by living organisms millions of years ago. Everything else is considered inorganic. In a few exceptional cases, living organisms produce inorganic materials, such as the calcium carbonate shells of marine organisms.
Crystalline Solids
Minerals are crystalline solids. Therefore, natural inorganic substances that are liquids are not minerals. For example, liquid water is inorganic, but it is not a mineral because it is a liquid. Even some solids may not be crystalline. A crystal is a solid in which the atoms are arranged in a regular, repeating pattern. The pattern of atoms in different samples of the same mineral is the same. Think about all of the grains of salt that are in a salt shaker. The atoms are arranged in the same way in
every piece of salt.
Chemical Composition
All minerals have a specific chemical composition. Minerals are either pure elements or chemical compounds. An element is a substance in which all of the atoms have the same number of protons. (Protons are the positive particles in the center of every atom, the nucleus.) You cannot change an element into another element by chemical means because the number of protons does not change. Silver, sodium, silicon, and oxygen are a few of the elements found in minerals. A few minerals are made of only one kind of element. The mineral silver is a pure element because it is made up of only silver atoms.
Most minerals, such as halite and quartz, are made up of chemical compounds. A chemical compound is a substance in which the atoms of two or more elements bond together. The elements in a chemical compound are in a certain ratio. Solid water (ice) is probably one of the simplest compounds that you know.
Minerals that are not pure elements are made of compounds. For example, the mineral quartz is made of the compound silicon dioxide, or SiO2. This compound has one atom of the element silicon for every two atoms of the element oxygen. When a mineral has a different chemical formula, it is a different mineral. For example, the mineral hematite has two iron atoms for every three oxygen atoms, while the mineral magnetite has three iron atoms for every four oxygen atoms. Many minerals contain more complex chemical compounds that are made of several elements. However, even the elements in more complicated compounds occur in certain ratios.
Structure of Minerals
The crystal structure of a mineral affects the mineral’s physical properties. Imagine you have three samples of halite. Each sample was found in a different country. They are all different sizes and shapes. They may have even been formed by different geologic processes. Will the samples all have the same crystal structure? Yes! All halite has the same chemical composition and the same crystal structure, despite physical differences.
Crystals in Minerals
The shape of the crystals of a mineral is determined by the way the atoms are arranged. When crystals grow large, you can see how the arrangement of atoms influences the shape. Large crystals only form when they have room to grow. Often, crystals are very small. Even if you cannot see the individual crystals in a mineral sample, the atoms are still ordered in a regular, repeating pattern.
This pattern can be used to help identify an unknown mineral sample. A trained scientist may be able to determine the crystal structure by the shape of a large crystal. If they cannot figure out the crystal structure by looking at the mineral, scientists use an instrument that uses X rays to find out how the atoms are arranged in a mineral sample.
A mineral has both a characteristic chemical composition and a characteristic crystal structure. Sometimes, minerals have the same chemical composition, but different crystal structures. What do you know about diamond and graphite? Diamonds are valued as gems for jewelry. They are also very hard. Graphite is used as pencil lead and has a slippery feel. Compare the diamond with the pencil lead. Diamond and graphite are both made of only carbon, but they are not the same mineral.
The crystal structure of diamond differs from the crystal structure of graphite. The carbon atoms in graphite bond to form layers. The bonds between each layer are weak, so the sheets can slip past each other. The carbon atoms in diamonds bond together in all three directions to form a strong network. As a result, the properties of diamond differ from the properties of graphite.
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