Characteristics of minerals and gems

Minerals are defined as solid, inorganic, naturally occurring substances with a definite chemical formula and general structure. Almost all chemical elements in the Earth's crust are associated with at least one mineral. They vary in color, hardness, density, crystal form, crystal size, transparency, composition, location, and abundance. Some minerals are radioactive (uranophane), while others are magnetic (magnetite). Some are uncombined elements, such as gold, silver, sulfur, bismuth, copper and platinum. Certain minerals, such as fluorite (calcium fluoride), glow with a vibrant luminescence after exposure to ultraviolet light. Feldspar (a potassium aluminum silicate) and quartz (silicon dioxide) are the most abundant minerals found in the Earth's crust. Mankind has coveted many minerals and gemstones due to their striking, beautiful colors. Some specimens of opal exhibit iridescent, rainbow-like colors within their crystals, while some specimens of the gemstone tourmaline show progressions of watermelon-like green to pink color from one side of a crystal to another. Although interesting, a few minerals are deceiving; many amateur prospectors have been tricked into thinking they have found gold, but have instead found pyrite (iron disulfide), otherwise known as "Fool's Gold" due to its uncanny resemblance to the precious metal. Diamond, the hardest natural substance found on Earth, has long been prized as the most desirable of all minerals due to its stunning interaction with light. Most diamonds, though, are impure and not suitable as gemstones; instead, they find industrial use as cutting tools, and are even made synthetically to meet this demand.

Credit: Dar Roberts, Department of Geography, University of California, Santa Barbara

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