礦物質的定義是什麼？（英文答案）

Minerals are natural compounds formed through geological processes. The term "mineral" encompasses not only the material's chemical composition, but also the mineral's structure. Minerals range in composition from pure elements and simple salts to very complex silicates with thousands of known forms (organic compounds are excluded). The study of minerals is called mineralogy.


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An assortment of minerals. Photo from US Geological Survey.
Mineral definition and classification
To be classified as a "true" mineral, a substance must be a solid and have a crystal structure. It must also be an inorganic, naturally-occurring, homogeneous substance with a defined chemical composition. The chemical composition may vary between end members of a mineral system. For example the plagioclase feldspars comprise a continuous series from sodium-rich albite (NaAlSi3O8) to calcium-rich anorthite (CaAl2Si2O8) with four recognized intermediate compositions between. Mineral-like substances that don't strictly meet the definition are sometimes classified as mineraloids. Other natural-occurring substances are Nonminerals. Industrial minerals is a market term and refers to commercially valuable mined materials (see also Minerals and Rocks section below).

A crystal structure is the orderly geometric spatial arrangement of atoms in the internal structure of a mineral. There are 14 basic crystal lattice arrangements of atoms in three dimensions, and these are referred to as the 14 "Bravais lattices". Each of these lattices can be classified into one of the six crystal systems, and all crystal structures currently recognized fit in one Bravais lattice and one crystal system. This crystal structure is based on regular internal atomic or ionic arrangement that is often expressed in the geometric form that the crystal takes. Even when the mineral grains are too small to see or are irregularly shaped, the underlying crystal structure is always periodic, and can be determined by X-ray diffraction.

Chemistry and crystal structure together define a mineral. In fact, two or more minerals may have the same chemical composition, but differ in crystal structure (these are known as polymorphs). For example, pyrite and marcasite are both iron sulfide, but their arrangement of atoms differs. Similarly, some minerals have different chemical compositions, but the same crystal structure: for example, halite (made from sodium and chlorine), galena (made from lead and sulfur) and periclase (made from magnesium and oxygen) all share the same cubic crystal structure.

Crystal structure greatly influences a mineral's physical properties. For example, though diamond and graphite have the same composition (both are pure carbon), graphite is very soft, while diamond is the hardest of all known minerals. This happens because the carbon atoms in graphite are arranged into sheets which can slide easily past each other, while the carbon atoms in diamond form a strong, interlocking three-dimensional network.

There are currently just over 4,000 known minerals, according to the International Mineralogical Association, which is responsible for the approval of and naming of new mineral species found in nature. Of these, perhaps 150 can be called "common," 50 are "occasional," and the rest are "rare" to "extremely rare."

What is a Mineral?
The following definitions on what constitutes a mineral were taken from several different sources and are arranged by year:



"A mineral is an element or chemical compound that is normally crystalline and that has been formed as a result of geological processes" (Nickel, E. H., 1995).

"Minerals are naturally-occurring inorganic substances with a definite and predictable chemical composition and physical properties." (O' Donoghue, 1990).

"A mineral is a naturally occurring homogeneous solid, inorganically formed, with a definite chemical composition and an ordered atomic arrangement" (Mason, et al, 1968).

"These... minerals ...can be distinguished from one another by individual characteristics that arise directly from the kinds of atoms they contain and the arrangements these atoms make inside them" (Sinkankas, 1966).

"A mineral is a body produced by the processes of inorganic nature, having usually a definite chemical composition and, if formed under favorable conditions, a certain characteristic atomic structure which is expressed in its crystalline form and other physical properties" (Dana & Ford, 1932).

"Every distinct chemical compound occurring in inorganic nature, having a definite molecular structure or system of crystallization and well-defined physical properties, constitutes a mineral species" (Brush & Penfield, 1898).





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What is a Mineral ?
Selected mineral definitions.


Crystallography
Mineral species by crystal system. New Java Crystal Models.


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Crystal Structures
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Mineral species and other structures with crystal structure data using the jPOWD applet. The jmol version is located here.


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X-Ray Powder Diffraction
Mineral species by intensity and D spacing.(400 kb)


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Chemical Composition
Mineral species by chemical elements selectable from a periodic table.


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New Dana Classification
Mineral species by New Dana system.


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Strunz Classification
Mineral species by Strunz system (courtesy of GEOLIB with updates from MinDAT, Athena, and MinMax).


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Determinative Mineralogy
Mineral species by physical and optical properties. Mineral species listed by calculated radioactivity.


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Alphabetical Listing
Mineral species listings.
A B C D E F G H I J K L M N O P Q R S T U V W Y X Z All


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Mineral Pictures
Mineral picture images. php/MySQL database.
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z


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Help Topics
Extensive help files which explain mineralogical terms and other features used in webmineral.com. Help on Mineral Name Pronunciations and Radioactivity


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Current Mineral News
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2006-12-07 Exceptional Minerals Minerals - Closeout Sale Tucson Gallery
2006-12-06 Greenside Minerals - New Minerals Added - Afghanistan and Pakistan
2006-12-05 John Betts Fine Minerals - Graves Mtn Rutiles
2006-12-04 Fabre Minerals - Post-Munich Update



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Other Links
Links to other sites with mineral data.


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Search the Mineralogy Database site. See examples.