There are various mineral riches in the soil, such as; Potassium, Iron, Magnesium, Sulphur and Calcium. Our Earth is the only planet with all the essential conditions required for the existence and survival of life. Natural resources available on the Earth and the energy obtained from the Sun are essential to fulfil the basic requirements of all life forms. Soil is one of the precious natural resources that contain weathered minerals and humus capable of supporting life.

The minerals riches in the soil supply various nutrients to life forms. These minerals remain locked up in the rocks hence cannot be available to the organisms. What are these minerals? How do these minerals riches in the soil become available for organisms? We will get to know all about this by reading the whole article.

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Soil Formation

Soil is the part of the Earth’s surface that consists of disintegrated rocks (inorganic matters) and decaying organic material. The gradual decomposition of inorganic matter (rocks) adds various minerals to the soil which are important in maintaining the life-supporting capacity of the soil. The formation of soil is a slow process that involves two steps:

1. Weathering
2. Paedogenesis

1. Weathering: It is the process of breakdown of large rocks into small minerals particles. Weathering occurs by the following three means:
a. Physical weathering: It involves the crushing of rocks by the following means:
heating, cooling,zing, abrasion by rains, wave action wind action, rolling stones, etc. Sun, water, and wind are three main factors that play important roles in physical weathering.

1. Sun: In the daytime, the rocks heat up due and expand due to solar radiation and contract at night. Since all pieces of the rocks do not contract and expand at the same rate, the cracks appear on the rocks and break up the rocks into small pieces.
2. Water: Water enters the cracks and onzing, the water expands. This creates pressure on the rocks and breaks the rock.
3. Winds: Strong winds form soil by continuously rubbing against rocks and eroding them.

Fig: Physical Weathering of Rocks

b. Chemical weathering: Hydrolysis, hydration, oxidation and reduction are the chemical processes involved in the weathering of the soil. The main end-products of chemical weathering are silica, clay, inorganic salts, and hydrated oxides.
c. Biological weathering: Biological weathering is done by lichens and mosses. Lichens living on the rocks produce acids that corrode the surface of rocks to form a thin layer of soil. The roots of trees sometimes enter the cracks and expand and lead to the breakdown of rocks.

2. Paedogenesis (soil development): It is the process of gradual degradation of organic matter by bacteria and fungi, leading to humification and mineralisation.

1. The process by which the detritus (dead remains of plants and animals) are converted into a dark-coloured amorphous substance (humus) in the soil is called humification.
2. Humus is very important for the fertility of the soil. It is a rich source of minerals for plants.
3. Detritivores, such as nematodes, earthworms, millipedes, mites, etc. consume organic matter and release nitrogen.
4. The process which results in the release of inorganic substances like carbon dioxide, nutrients (NH₄⁺, Mg⁺⁺, Ca⁺⁺, etc.) is called mineralisation.

The weathered and paedogenesis of rock thus represent four distinct horizontal planes that represent the soil profile.

Soil Profile

Soil profile represents the vertical section of the Earth’s crust that is made up of a succession of horizontal layers (horizons). Each of which varies in thickness, colour, texture, structure, consistency, porosity, acidity, and composition. A-horizon is the topsoil made up of litter and humus. B-horizon is composed of mineral soil. C-horizon contains unconsolidated parent material. D-horizon comprises rock and unmodified parental material.

Fig: Soil Profile

Soil Composition

1. Mineral Matter: 45 – 60%
2. Organic Matter: 5 – 10% (living organisms, humans, roots of plants)
3. Air: 15 – 25%
4. Water: 25 – 35%

Fig: Soil Composition

Soil Minerals

Types of Soil Minerals: Minerals constitute the largest portion of the soil. Soil minerals can be divided into the following two categories:

1. Primary minerals in the soil: The minerals that have not been chemically transformed since the deposition are called primary minerals in the soil. These mainly include silica minerals, iron minerals, apatite, volcanic gases, non-crystalline organic constituents.
2. Secondary minerals in the soil: These are the minerals that are formed by the weathering of rocks (primary minerals). Hydroxides, carbonates, sulphates, phosphates, halides, etc. are examples of secondary minerals.

Soil Forming Minerals

Oxygen, silicon, iron, calcium, aluminium, sodium, potassium, and magnesium are the main elements that make up most of the minerals. Some of the soil-forming minerals are discussed below:

1. Haematite: It is a reddish-black coloured mineral ore that is a derivative of the iron element. It can easily absorb the water and form ferric oxide.
2. Limonite: It is a brownish-black coloured iron ore that serves as a source of ocher and umber pigments.
3. Magnetite: It is an iron ore that is more magnetic than any other iron ore.
4. Siderite: It is a valuable iron mineral found in waterlogged soil. It contains about 48% of iron. The colour of this mineral ore ranges from yellow to dark brown.
5. Goethite: It is a derivative of limonite, pyrite; therefore it can be said as a weathered product of other iron oxides. It is well known for its use as a pigment.
6. Gibbsite: It is an important ore of aluminium. It is found in highly weathered soils and has been attributed to direct precipitation from soil solutions.
7. Calcite: It is a carbonate mineral. It is most commonly found in sedimentary rocks. It exhibits a variety of colours, such as White, Yellow, Red, Orange, Blue, Green, Brown, Gray etc.
8. Dolomite: It is a type of limestone that is rich in magnesium and calcium carbonate. Besides these, it also contains some other mineral elements in trace amounts.
9. Gypsum: It is the commonly known sulphur mineral that is found in sedimentary rocks.
10. Pyrite: It is a bright yellow mineral ore that has a chemical composition of iron sulphide. It is also extracted from the sedimentary rocks.

Nutrient Element Constituents	Minerals Ores (Riches in the Soil)
Iron oxides	Hematite, Goethite, Magnetite, Limonite, Maghemite, Lepidocrocite, Ferrihydride
Aluminium oxides	Gibbsite
Carbonates	Azurite, Malachite, Calcite
Halides	Fluorite
Phosphate	Turquoise
Sulphates	Gypsum
Sulphides	Pyrite

Fig: Different Types of Soil Minerals made of Mineral elements

Uses of Soil Minerals

Uses of mineral elements in plants and humans:
Soil minerals primarily contribute to soil fertility that promotes agricultural production. There are the following uses of different mineral elements in plants and humans:

1. Nitrogen is an essential constituent of different proteins, nucleic acids, vitamins, and hormones.
2. Phosphorus is a constituent of the plasma membrane, certain proteins, nucleic acids, nucleotides. It plays an essential role in energy transfer reactions.
3. Potassium is involved in many physiological activities like photosynthesis, respiration, chlorophyll, and protein synthesis.
   Nitrogen, Phosphorus, and Potassium (NPK) contribute to soil fertility and are primarily absorbed by plants.
4. Calcium is required for the formation of spindle fibres during cell division. It regulates several metabolic activities.
5. Calcium is the main constituent of our teeth and bones.
6. Magnesium activates the enzymes involved in respiration and photosynthesis. It is also a constituent element of chlorophyll and maintains ribosome structures.
7. Sulphur increases root development and nodule formation.
8. Iron is an important constituent of certain proteins and blood.
9. Zinc is required for the synthesis of auxin.
10. Gypsum is used as fertilisers and also used to make plasters that are used in the construction of buildings.

Industrial and Agricultural Uses of soil minerals
There are several other uses of secondary minerals that can be described as follows:

1. Haematite is a red coloured mineral that is used to produce gemstones, beads, small sculptures, tumbled stones, and other items.
2. Goethite is considered the most important ore of iron after haematite. One of the most prominent applications of goethite is in eliminating the chemical element, cadmium, from polluted water bodies.
3. Magnetite is used for steel manufacture. It is also used as a catalyst in the harbour process of making ammonia. Besides this, it is used as a colouration of paint and ceramics.
4. Limonite has been used as a yellow or brown colour pigment in paintings since prehistoric times. It is an inexpensive catalyst for various industrial processes such as contaminant decomposition, ammonia removal and coal liquefaction.
5. Gibbsite is used for the production of aluminium metal.
6. Azurite and malachite are used for ornamental purposes such as making beads and jewellery.
7. Fluorite has a wide range of uses. It is primarily used in the metallurgical, ceramic, and chemical industries. However, cutting, and polishing stones are the other uses.
8. Calcite is used for the production of cement and agricultural soil treatment.
9. Gypsum is used for manufacturing wallboard, cement, and plaster of Paris. It is also used for soil conditioning.

Summary

Soil is an edaphic factor. It is a house of several minerals and mineral elements that are essential for plants and animals. Primarily the soil minerals remain deposited in the rocks and cannot be utilised for plant and animal welfare. Soil weathering and soil development (paedogenesis) make the soil minerals available for plant and animal usage. Plants utilise these minerals for synthesising food, growth. Besides this, mineral elements synthesise several life-supporting elements such as haemoglobin, nucleic acids, proteins, etc. Moreover, these also regulate several physiological activities. This article covers the detailed study of soil minerals and their uses.

FAQs

Q.1. How Mineral-rich soil is formed?
Ans: Mineral-rich soil is formed by the process of weathering and paedogenesis.

Q.2. What percentage of soil are minerals?
Ans: Minerals constitute about 45 – 60% of the soil.

Q.3. What is the oldest mineral on the Earth?
Ans: Zircon is the oldest mineral on the Earth.

Q.4. What are the five soil types?
Ans: Sandy, Clay, Slit, Peat, and Loamy are the five main types of soil.

Q.5. What minerals do plants absorb from the soil?
Ans: Plants mainly absorb nitrogen, phosphorus, potassium from the soil. Besides these, plants also absorb magnesium, sulphur, iron, etc. in small amounts.

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