Maarg Manthan · Topic 2.1

Minerals: Major Elements of the Earth’s Crust

Geography › Geology – Minerals and Rocks · Topic 2.1

A mineral is a naturally occurring, inorganic, solid substance with a definite chemical composition and an ordered internal crystal structure. The Earth's crust is made mostly of eight elements: oxygen (46.6 per cent by weight), silicon (27.7), aluminium (8.1), iron (5.0), calcium (3.6), sodium (2.8), potassium (2.6) and magnesium (2.1). These combine into minerals, and the silicates, built on silicon and oxygen, make up over 90 per cent of the crust. Only about thirty of the several thousand known minerals form most of the rocks.

5 min read · UPSC Prelims · Geography · Geology – Minerals and Rocks

At a Glance

Most abundant element Oxygen, 46.6 per cent
Second element Silicon, 27.7 per cent
Eight elements About 98.5 per cent of the crust
Largest mineral group Silicates
Most common mineral Feldspar
Exam link UPSC Prelims, Geography: Geology – Minerals and Rocks

Where Does It Fit?

This is the first topic of the macro on minerals and rocks. It names the elements that make the crust and the minerals they form, which are then used to describe rocks, landforms and soils in the rest of the macro. Previous topic: Tropic of Cancer Winter solstice About 22 December, Sun over the…">Equinoxes and Solstices (Summer Solstice, Winter Solstice, Vernal and Autumnal Equinox). Next topic: Physical Characteristics of Minerals (Crystal Form, Cleavage, Fracture, Lustre, Colour, Streak, Hardness, Specific Gravity).

What Is a Mineral?

In short: a mineral is a natural, non-living solid with a fixed chemical make-up and a regular arrangement of atoms.

Naturally occurring: it forms by natural processes, not in a factory.
Inorganic: it is not made by living things, so coal and oil are not minerals.
Solid: water is not a mineral, though ice is.
Definite composition: it has a chemical formula, such as SiO2 for quartz and NaCl for rock salt.
Crystal structure: atoms are arranged in a regular, repeating pattern.

About 6,000 mineral species are known, but most are rare. Minerals are not the same as ores. An ore is a mineral or rock from which a metal can be extracted at a profit, such as hematite for iron or bauxite for aluminium.

Which Elements Make Up the Earth’s Crust?

Element	Symbol	Share of crust by weight (per cent)	Found mainly in
Oxygen	O	46.6	Almost all minerals, especially silicates and oxides
Silicon	Si	27.7	Quartz, feldspar, mica
Aluminium	Al	8.1	Feldspar, clay, bauxite
Iron	Fe	5.0	Hematite, magnetite, pyroxene
Calcium	Ca	3.6	Calcite, feldspar, gypsum
Sodium	Na	2.8	Feldspar, rock salt
Potassium	K	2.6	Feldspar, mica
Magnesium	Mg	2.1	Olivine, pyroxene, dolomite

Together these eight elements form about 98.5 per cent of the crust. Metals such as copper, lead, gold and tin are rare in the crust, and become useful only where natural processes have concentrated them. The mantle and core differ in make-up, as shown in Layered Structure of the Earth (Five Layers).

What Are the Main Groups of Minerals?

Group	Basis	Examples
Silicates	Silicon and oxygen, often with Al, Fe, Mg, Ca, Na, K	Quartz, feldspar, mica, olivine, pyroxene, amphibole, clay minerals
Oxides	Metal and oxygen	Hematite, magnetite, bauxite, corundum
Carbonates	Carbon and oxygen	Calcite, dolomite
Sulphides	Metal and sulphur	Pyrite, galena, sphalerite, chalcopyrite
Sulphates	Sulphur and oxygen	Gypsum, barite
Halides	Chlorine or fluorine	Rock salt (halite), fluorite
Native elements	A single element	Gold, silver, copper, sulphur, graphite, diamond

Silicates make up over 90 per cent of the crust. The building block is the silicon-oxygen tetrahedron, one silicon atom surrounded by four oxygen atoms, which links with others in chains, sheets and frameworks. Feldspars, which are silicates of aluminium with potassium, sodium or calcium, are the most abundant group of minerals and form about half the crust. Quartz, which is pure silicon dioxide, is the second most common.

Which Minerals Form Most Rocks?

Only about thirty minerals, called rock-forming minerals, make up the bulk of the common rocks. The main ones are feldspar, quartz, pyroxene, amphibole, mica and olivine, together with calcite in limestones and clay minerals in shales.

Feldspar: the most common; light-coloured, in granite and basalt.
Quartz: hard, glassy, resistant to weathering; the main mineral of sand.
Mica: splits into thin sheets; used in electrical goods; India is a leading producer.
Pyroxene and amphibole: dark minerals of iron and magnesium, in basalt and gabbro.
Olivine: green mineral of iron and magnesium; the main mineral of the upper mantle.

Their physical properties are described in Physical Characteristics of Minerals (Crystal Form, Cleavage, Fracture, Lustre, Colour, Streak, Hardness, Specific Gravity), and their combinations into rocks in Rocks as Aggregates of Minerals; Petrology. As an analytical point, the crust is mainly oxygen and silicon, which is why most of the surface of the Earth is silicate rock.

Why Is This Topic Important?

Facts Percentages of elements are asked
Base Foundation for rocks, soils and resources
Concept Mineral versus ore versus rock

What Came Next?

The next topic explains the properties by which minerals are told apart, such as hardness, lustre and cleavage. Next topic: Physical Characteristics of Minerals (Crystal Form, Cleavage, Fracture, Lustre, Colour, Streak, Hardness, Specific Gravity).

Key People and Terms

Mineral Natural inorganic solid with a fixed composition
Ore Mineral from which metal can be extracted
Silicate Mineral containing silicon and oxygen
Feldspar Most abundant mineral group
Native element Mineral made of one element
Rock-forming mineral Mineral that makes common rocks

Exam Corner

Points to Remember

Oxygen 46.6 and silicon 27.7 per cent.
Aluminium is the most abundant metal in the crust.
Feldspar is the most abundant mineral group.
Silicates make up over 90 per cent of the crust.
Coal and oil are not minerals in the strict sense.

Do Not Confuse With

Mineral and rock One substance versus an aggregate of minerals
Mineral and ore Natural substance versus one worth mining
Silica and silicon Silicon dioxide versus the element

Memory Hook

Oh So All Fine Cooks Never Know Magic: O, Si, Al, Fe, Ca, Na, K, Mg.

Mains Angle

Questions link mineral wealth to geology. These points add depth.

Abundance Common versus rare elements
Concentration Why ores are found only in places
Use Industry and construction

A Question You May Face

An original practice question, not a past paper question.

“Describe the elemental composition of the Earth’s crust and explain why only a few minerals form most of its rocks.”

How to Answer

Elements Eight with shares.
Groups Silicates and others.
Rock-forming Feldspar, quartz and mica.
Link Ores and resources.

GS Relevance

Prelims: eight elements of the crust and their percentages, silicates, feldspar and quartz, mineral groups. GS Paper 1: distribution of key natural resources.

Frequently Asked Questions

Which elements make up most of the Earth's crust?

Eight elements make up about 98.5 per cent of the crust by weight: oxygen (46.6), silicon (27.7), aluminium (8.1), iron (5.0), calcium (3.6), sodium (2.8), potassium (2.6) and magnesium (2.1). Oxygen and silicon alone form nearly three-fourths of it.

What is a mineral?

A mineral is a naturally occurring, inorganic, solid substance with a definite chemical composition and a regular crystal structure. Quartz, feldspar, calcite and gold are minerals. Coal and petroleum are not minerals, because they come from the remains of living things.

What is the difference between a mineral and an ore?

A mineral is any naturally formed inorganic solid of definite composition, while an ore is a mineral or rock from which a metal can be extracted at a profit. All ores contain minerals, but most minerals are not ores, because they are too scarce or too costly to process.

Which is the most abundant mineral group in the crust?

The silicate group is the most abundant, making up over 90 per cent of the crust. Among silicates, feldspars are the most common minerals, forming about half of the crust, and quartz is the second most common. They are built from silicon-oxygen units.

Which metal is most abundant in the Earth's crust?

Aluminium is the most abundant metal in the crust, forming about 8.1 per cent by weight, followed by iron at about 5 per cent. However, aluminium occurs combined in silicates and clays, and only its ore bauxite is economic to mine.

PYQ Practice — Statement Analysis

1 Oxygen is the most abundant element in the Earth's crust by weight.

True

It forms about 46.6 per cent.

2 Iron is the most abundant metal in the crust.

False

Aluminium is more abundant.

3 Coal is a mineral in the strict sense.