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3.1.1. What is a mineral?

The minerals

The earth's crust is made up of rocks, solid materials made up of different minerals.

Although there are more than 5,300 known minerals, only about 20 are the most abundant and the main constituents of rocks are the so-called petrogenetic minerals.

What is a mineral?

mineral is a natural and homogeneous solid, generally formed by inorganic processes, with an orderly internal arrangement and with a chemical composition and physical properties that are either fixed or vary within a defined range, and therefore, limited.

It is necessary to clarify some terms of this definition of mineral:

  • Solid: Excludes liquid and gaseous substances from the definition. For example, when water is crystallized into ice it is a mineral , but it is not if it is in a liquid state.
  • Natural: Formed by geological processes. A man-made substance cannot be considered a mineral even if it meets the other conditions of the definition, such as a synthetic diamond .
  • Homogeneous: Each mineral has the same chemical composition in all its parts.
  • Of inorganic origin: Minerals are not considered if they are caused by the activity of living beings.
  • Characteristic chemical and physical properties: Minerals have a characteristic chemical composition, which allows them to be represented by a chemical formula. Having a certain chemical composition and structure makes them have certain physical properties.
  • Orderly internal layout. They are said to have a crystalline structure because the components of a mineral are ordered.

The elements that are part of a mineral are arranged in an orderly manner. A crystal is a mineral that has an orderly internal structure. Sometimes, the internal order that a crystal presents can also be manifested on the outside, with very striking shapes.

If when it solidifies, the components are not ordered, the crystalline structure will not form. Instead, a glass will have formed and is said to have a glassy structure.

Interactive activity: Difference between crystal, mineral and rock.

How are minerals formed?

The minerals that make up the rocks of the earth's crust can be formed in several ways:

  • By precipitation

Water contains dissolved substances and, when evaporation occurs , the mineral precipitates. For example, plaster or halite.

  • By solidification

When magma cools, its components unite to form minerals, such as quartz, feldspar and mica (which form granite), olivine, etc.

  • By sublimation

In volcanic areas some minerals can be formed directly from gases.