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What is the difference between a rock and what is a mineral?

A mineral, by definition, is any naturally occurring, inorganic substance, often additionally characterized by an exact crystal structure. Its chemical structure can be exact, or can vary within limits. Native elements that occur naturally are also considered minerals.

All minerals belong to a chemical group, which represents their affiliation with certain elements or compounds. The classified chemical groups are known as: Elements, Sulfides, Oxides, Halides, Carbonates, Nitrates, Borates, Sulfates, Chromates, Phosphates, Arsenates, Vanadates, Tungstates, Molybdates, and Silicates. Some of these chemical groups have sub-categories, which may be categorized in some mineral references as separate groups.

All minerals belong to one of the six crystal groups, classified according to the way the atoms of the mineral are arranged. Minerals also have distinctive properties, such as color, hardness, crystal habit, specific gravity, luster, fracture, and tenacity. Many of these properties can vary among a single mineral, within limits. Many minerals exhibit certain properties that others do not, such as fluorescence and radioactivity.

Minerals are an economic commodity; they are mined because of the need for a valuable element they contain or an intrinsic property they may have. Other minerals are mined for their beauty and rareness, thus giving many specimens an accepted worldwide value. There are well over 3,000 scientifically classified different types of minerals, and new ones are always being discovered. The vast majority are not known to professional mineral collectors, because they are rare, have no economic purpose, and for the most part do not make good specimens.

There is a class of substances known as "mineraloids". While not truly falling into the category of minerals, they are still usually classified as minerals. Two well-known examples are Mercury, which lacks a crystal structure due to its liquid state, and Opal, which also lacks a crystal structure as well as a definitive chemical formula. Despite the fact that these mineraloids lack certain essential characteristics of minerals, they are nevertheless classified as minerals in most reference guides including the acclaimed Dana's System of Minerology. Another unique category of minerals is the organic minerals. While this term is technically an oxymoron, since the definition of a mineral requires it to be inorganic, there are several naturally occuring rare organic substances with a definitive chemical formula. The best known example of this is Whewellite. Most reference guides and scientific sources make an exception to these substances and still classify them as minerals.

What is a Rock?

A rock is an indefinite mixture of naturally occurring substances, mainly minerals. Its makeup may vary in containment of minerals and organic substances, and its composition is never exact. Rocks can be composed of tiny microscopic grains of minerals or organic substances to coarse mineal agglomerates where the individual minerals are easily discernible. Rocks may range in size from tiny pebbles to huge mountains. Rocks make up the earth's crust. Many rocks are not solid, such as magma, soil, and clay. Different mineral deposits can be found in related rock formations, providing use by estimating what minerals rock formations may contain.

The term "rock collection" is usually misused for "mineral collection". Although a few people collect rocks, the amount of people collecting minerals is far greater.


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