Groups of minerals - Imagine you were in charge of organizing more than 100 minerals for an exhibit at a museum near you. You want the people who visit your exhibit to learn as much as possible about the minerals they see. How would you group the minerals together in your exhibit? Mineralogists are scientists who study minerals.
They use a system that divides minerals into groups based on chemical composition and structure. Even though there are over 4,000 minerals, most minerals fit into one of eight mineral groups. Minerals with similar crystal structures are grouped together.
Silicate Minerals
Silicate minerals make up over 90 percent of Earth’s crust. When you think of the Earth’s crust, you may think of the people, animals or trees that live on the Earth’s surface. Yet living organisms are made of organic matter and there is only a small amount of organic matter in Earth’s crust. About 1,000 silicate minerals have been identified, making the silicate minerals the largest mineral group.
Silicates are minerals that contain silicon atoms bonded to oxygen atoms. The basic building block for all silicate minerals is called a tetrahedron, where one silicon atom is bonded to 4 oxygen atoms. Silicate minerals also often contain other elements, such as calcium, iron, and magnesium.
Notice that the silicon and oxygen form a shape like a pyramid; this is the tetrahedron. The pyramid-shaped building blocks can combine together in numerous ways. The silicate mineral group is divided into six smaller groups, which are determined by the way the siliconoxygen building blocks join together. The pyramids can stand alone, form into connected circles called rings, link into single and double chains, form large flat sheets of pyramids or join in three dimensions.
Feldspar and quartz are the two most common silicate minerals. Beryl is a silicate mineral, which forms rings from the tetrahedra. The gemstone emerald is a type of beryl that is green because of chemical impurities. Biotite is a mica, which is another silicate mineral that can be broken apart into thin, flexible sheets.
Native Elements
Native elements are minerals that contain only atoms of one type of element. The elements are not combined with other elements. In nature most elements are combined with other elements to form chemical compounds. So, the native elements mineral group contains a relatively small number of minerals. Some of the minerals in this group are rare and valuable. Gold, silver, sulfur, and diamond are examples of native elements.
Carbonates
From the name “carbonate,” what would you guess carbonate minerals contain? If you guessed carbon, you would be right! More specifically, all carbonates contain one carbon atom bonded to three oxygen atoms. Carbonates may include other elements, such as calcium, iron, and copper.
Carbonate minerals are often found in areas where ancient seas once covered the land. Some carbonate minerals are very common. Calcite is one such mineral. Calcite contains calcium, carbon, and oxygen. Have you ever been in a limestone cave or seen a marble tile? Calcite is in both limestone and marble. Azurite and malachite are also carbonate minerals, but they contain copper instead of calcium. They are not as common as calcite, they are very colorful.
Halides
Halide minerals are salts that can form when salt water evaporates. This mineral class includes more than just table salt. It includes minerals that contain the elements fluorine, chlorine, bromine, or iodine. These elements combine with metal elements. Halite is a halide mineral that contains the elements chlorine and sodium. Fluorite is another type of halide that contains fluorine and calcium. Fluorite can be found in many colors. If you shine an ultraviolet light on some samples of fluorite, they will glow!
Oxides
Earth’s crust contains a lot of oxygen, which combines with many other elements. Oxides are minerals that contain one or two metal elements combined with oxygen. Oxides are different from silicates because oxides do not contain silicon. Many important metals are found as oxides. For example, hematite and magnetite are both oxides that contain iron. Hematite (Fe2O3) has a ratio of two iron atoms to three oxygen atoms. Magnetite (Fe3O4) has a ratio of three iron atoms to four oxygen atoms. You might have noticed that the word magnetite contains the word magnet. Magnetite is a magnetic mineral.
Phosphates
Phosphates have a tetrahedron building block that is similar to that of the silicates. But, instead of silicon, phosphates have an atom of phosphorus, arsenic, or vanadium bonded to oxygen. Although there are many minerals in this group, most of the minerals are rare. The chemical composition of these minerals tends to be more complex than some of the other mineral groups. Turquoise is a phosphate mineral that contains copper, aluminum, and phosphorus. It is rare and is used to make jewelry.
Sulfates
Sulfate minerals contain sulfur atoms bonded to oxygen atoms. Like halides, they can form in places where salt water evaporates. Many minerals belong in the sulfate group, but there are only a few common sulfate minerals. Gypsum is a common sulfate mineral that contains calcium, sulfate, and water. Gypsum is found in various forms. For example, it can be pink and look like it has flower petals. However, it can also grow into very large white crystals.
Sulfides
Sulfides contain metal elements combined with sulfur. Unlike sulfates, sulfides do not contain oxygen. Pyrite, a common sulfide mineral, contains iron combined with sulfur. Pyrite is also known as fool’s gold. Gold miners have mistaken pyrite for gold because the two minerals look so similar.
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