If you are confused about the use of the word mineral, or you are having a difficult time determining what a mineral is, you're not alone. There are many definitions of the word "mineral." The Glossary of Geology (Bates and Jackson, 1980, p. 401) defines a mineral as "a naturally occurring inorganic element or compound having an orderly internal structure and characteristic chemical composition, crystal form, and physical properties." Minerals differ from rocks, which are naturally occurring solids composed of one or more minerals. Rocks do not have a distinctive chemical composition or crystal structure. The earth science definition, however, is not always used to define minerals.Legal definition
The legal definition of "mineral," according to Black's Law Dictionary (1968, p. 1146) is "any valuable inert or lifeless substance formed or deposited in its present position through natural agencies alone, and which is found either in or upon the soil of the earth or in the rocks beneath the soil." This is a much broader definition of mineral than the earth science definition. When used this way, the word may include minerals as geologically defined, rocks as geologically defined, and sediment (gravel, sand, clay). In some contexts, it might even include water. Yet Black's Law Dictionary (1968, p. 1146) also notes that "the word is not a definite term and is susceptible of limitations or extensions according to intention with which it is used." This means that even the legal definition is subject to different meanings for different uses.U.S. government definition
The federal government defines minerals in its section on national mining and minerals policy (U.S. Code: Title 30, Section 21a) as including all minerals and mineral fuels including some non-solid substances such as petroleum and natural gas. This definition is problematic, in that it uses the word "minerals" in the definition of the word "mineral." It also includes petroleum and natural gas, which are not considered minerals if the earth science definition is used. As in the legal definition, water could be considered a mineral in some areas, depending on the statute and legal issue being considered.
The U.S. Geological Survey publishes an annual Minerals Yearbook, which includes mineral commodities summaries. Mineral commodities include minerals as defined in earth sciences, but also manufactured products such as abrasives, cement, and lime. Still confused?Economic definitions
When economists, engineers, and scientists use the word "mineral" in an economic context, they generally use the terms "industrial minerals" or "mineral resources." The term "mineral resources" refers to the occurrence of any mineral commodity (as defined above) that could be removed from the ground. There are three categories of mineral resources: fuels minerals, metallic minerals (also called ore minerals), and industrial or construction minerals. The term "fuels minerals" refers to natural gas and petroleum, so means minerals as defined by the federal government, but not minerals as geologically defined. The term "metallic minerals" (for example, iron ore, copper) almost always also refers to minerals as geologically defined. The term "industrial minerals" may include minerals as geologically defined, but more often includes rocks (for example, limestone) and sediments (for example, sand and clays) as geologically defined.Biological-medical definition
The biological and health definition of minerals is what you are using when you say "vitamins and minerals." In this context, the word "mineral" is used to describe naturally occurring nutrients, which are inorganic elements and compounds such as iron, potassium, and calcium. These do not include rocks or fossil fuels, although the minerals used in vitamins may be derived from rocks and fossil fuels. The health definition is still slightly different from the earth science definition, because it can include free elements such as calcium. In geology (and other sciences), calcium is considered an element that can be combined into a naturally occurring solid with a distinct crystal structure, such as calcite, which would be considered a mineral using the earth science definition.