A mineral is a substance found in nature. Its chemical composition is fixed, even if it sometimes contains a pollutant that changes its colour. It is inorganic and has a fixed geometrical structure, that is why it is solid. It has a certain crystalline structure. The study of minerals is called mineralogy, and there are more than 5,000 known mineral species.
They can be distinguished by various physical and chemical properties. There are different species depending on their chemical composition and crystalline structure. The geological environment influences the properties of the mineral.
Classification of minerals
In order to classify minerals, it is not only convenient to classify them by their chemical composition, but also by their structural principles. On this basis, minerals are classified as follows:
- Native elements
- Oxides and hydroxides
- Carbonates, nitrates and borates
- Sulphates and chromates
- Tungsulfates and molybdates
- Phosphates, arsenates and vanadates
These are the minerals that can be found in nature in their pure state. They are divided into metallic and non-metallic.
The elements belonging to this group belong to the same family in the periodic classification of the elements, so their atoms have similar chemical properties. In addition, they are all sufficiently inert to be found in the elemental state in nature. In this type of ore, extraction is carried out to obtain a particular metal. There are four types:
- Basic (copper, zinc, lead...).
- Ferrous (iron, cobalt, chromium...).
- Precious (silver, gold...).
- Radioactive (radium, plutonium...).
These minerals are of great value for trade and industry. They are extracted from mineral resources that after treatment have different uses: saltpetre, iodine, lithium salts, gypsum, iron oxide, cement, lime, phosphates, sulphur, aluminium sulphate, alumina, bauxite, chromite...
Silicates make up about one third of all known minerals. They are the most important ceramic materials as they contribute to our civilisation and standard of living (stones, cement or glass). The predominant silicate minerals are silicon and oxygen, as they make up the majority of the earth's crust. Other common elements in the earth's crust are aluminium, iron, magnesium, sodium, calcium and potassium.
The most important silicates are: feldspars, olivines, amphiboles, quartz, micas, granites and pyroxenes.
Non-silicate minerals are divided into different classes: native elements, organic compounds, oxides and hydroxides, sulphides, carbonates and nitrates, phosphates, halides, borates and sulphates.
This classification includes sulpharsenides, arsenides, and tellurides. Most of them are recognisable because they are opaque, have a metallic lustre and distinctive colours. Examples of sulphides are: chalcocite, galena, acanthite, sphalerite, cinnabar or bornite pyrrhotite.
In this group of minerals, sulphur takes the place of oxygen in the most common and best known oxygenated acids, such as carbonic acid, sulphuric acid or phosphoric acid. Sulphosalts are an important mineral type because they can indicate a number of sulphur minerals other than sulphides. Many species in this group are rare, are closely associated with other similar minerals and are often imperfectly crystallised. Some of them are livingstonite, techmanite, zinkenite or miargyrite.
Oxides and hydroxides
These are natural compounds in which the oxygen is combined with one or more metals.
Oxides are a group of relatively hard, dense and refractory minerals. Hydroxides tend to be less hard and of lower density, and usually occur as secondary alloys or as weathering products.
This group consists of chemical combinations of metals with halogens such as fluorine, chlorine, iodine or bromine. They have low hardness, low specific gravity, and a glassy lustre. Examples are sylvinite, halite or fluorspar.
Carbonates, nitrates and borates
Carbonates are minerals formed by the chemical combination of a metal with the anionic carbonate group. The most prominent are the calcite group, aragonite and dolomite.
Nitrates, which occur rarely in nature, are readily soluble in water. The most important are nitro and nitratine.
Borate minerals are rarely found in industrial deposits. Most of them have a low weight and a glassy or greasy lustre.
Sulphates and chromates
Sulphate formation occurs under conditions of high oxygen concentration, i.e. at high oxygen partial pressure in the environment and at relatively low temperatures. Examples are celestine or gypsum.
Tungstenates (tungstenates) and molybdates
This small group of ore minerals are colourful and very interesting. Tungsten (W) has a much higher atomic weight (184) than molybdenum (96), both belong to the same family of the periodic table and have the same ionic radius. Therefore, they can easily substitute for each other as the coordinating cation.
Types include tungstenite, scheelite and wulfenite.
Applications and uses
Minerals are very important because they are applied in different activities. Some minerals are used in the same way they are extracted; sulphur, salt... but others have to undergo certain processes to obtain the product; aluminium, copper... Minerals are the source of metals.
Minerals are obtained from mines where the required material is extracted. There are 2 types of mines:
- Opencast mines: the ore can be drilled or blasted and is loaded onto trucks. They are mined in spiral terraces.
- Underground mines: rock is drilled or blasted in a controlled manner. There are shafts leading down to horizontal galleries.
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