NAICS 21 is the category within the North American Industry Classification System which is composed of establishments that extract naturally occurring mineral

Mineral

A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...

 solids(i.e. as metal

Metal

A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...

s, coal

Coal

Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

 and other industrial minerals

Industrial minerals

Industrial minerals are geological materials which are mined for their commercial value, which are not fuel and are not sources of metals ....

), liquid minerals (i.e. crude petroleum) and gas

Gas

Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

es (i.e. natural gas

Natural gas

Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

).

Definition of mining

NAICS 21 uses the term "mining" to include quarry

Quarry

A quarry is a type of open-pit mine from which rock or minerals are extracted. Quarries are generally used for extracting building materials, such as dimension stone, construction aggregate, riprap, sand, and gravel. They are often collocated with concrete and asphalt plants due to the requirement...

ing, well operations, beneficiating

Mineral processing

In the field of extractive metallurgy, mineral processing, also known as mineral dressing or ore dressing, is the process of separating commercially valuable minerals from their ores.-History:...

 and other mineral preparation customarily performed at the mine sites, or as a part of mining activity and distinguishes two basic activities:

Mine operation

Mine operation includes companies that operate mines, quarries, or oil and gas wells for themselves, and companies which operate them on a contract

Contract

A contract is an agreement entered into by two parties or more with the intention of creating a legal obligation, which may have elements in writing. Contracts can be made orally. The remedy for breach of contract can be "damages" or compensation of money. In equity, the remedy can be specific...

 or fee basis.

Mining support activities

Mining support activities include companies that perform exploration

Mineral exploration

Mineral exploration is the process of finding ore to mine. Mineral exploration is a much more intensive, organized and professional form of mineral prospecting and, though it frequently uses the services of prospecting, the process of mineral exploration on the whole is much more involved.-Stages...

 (except geophysical survey

Geophysical survey

Geophysical survey is the systematic collection of geophysical data for spatial studies. Geophysical surveys may use a great variety of sensing instruments, and data may be collected from above or below the Earth's surface or from aerial or marine platforms. Geophysical surveys have many...

ing) and other mining services, on a contract or fee basis, with the exception of mine site preparation and construction of oil/gas pipelines.

Further breakdown

Companies are grouped and classified according to the natural resource

Natural resource

Natural resources occur naturally within environments that exist relatively undisturbed by mankind, in a natural form. A natural resource is often characterized by amounts of biodiversity and geodiversity existent in various ecosystems....

 which is or will be mined. Industries include establishments that develop the mine site, extract the natural resources, and/or those that process the mineral mined.

Smelting and refining

Smelting

Smelting

Smelting is a form of extractive metallurgy; its main use is to produce a metal from its ore. This includes iron extraction from iron ore, and copper extraction and other base metals from their ores...

 and refining

Refining

Refining is the process of purification of a substance or a form. The term is usually used of a natural resource that is almost in a usable form, but which is more useful in its pure form. For instance, most types of natural petroleum will burn straight from the ground, but it will burn poorly...

 take place in both the "mineral processing" (NAICS 21) stages and the manufacturing stages (NACIS 31-31).