Chapter 5 – Minerals and Rocks

What is a mineral?
A mineral is a naturally occurring inorganic substance with a definite chemical composition and atomic structure. They form through geological processes and can be solid, crystalline, or amorphous.

How are minerals classified?
Minerals are classified based on their chemical composition: silicates, oxides, sulphides, carbonates, halides, and native elements like gold and silver.

What are silicate minerals?
Silicates are the most abundant minerals on Earth. They contain silicon and oxygen, often combined with metals. Examples: quartz, feldspar, mica.

What are oxides?
Oxide minerals consist of oxygen and a metal. Common examples are hematite (iron ore) and bauxite (aluminum ore).

What are sulphides?
Sulphide minerals are composed of sulphur and metals. Examples include galena (lead ore) and pyrite (iron sulphide).

What are carbonate minerals?
Carbonates contain carbonate ions (CO₃²⁻). Examples: calcite and dolomite, often found in sedimentary rocks like limestone.

What are native elements?
These minerals occur in pure form. Examples include gold, silver, platinum, and copper.

How are minerals formed?
Minerals form through crystallization from magma, precipitation from solutions, changes in pressure and temperature, and biological activity.

What is a rock?
A rock is a naturally occurring aggregate of minerals. It can be hard (granite) or soft (chalk) and forms the solid part of Earth’s crust.

How are rocks classified?
Rocks are classified into three types based on origin: igneous, sedimentary, and metamorphic.

What are igneous rocks?
Formed from solidified magma or lava. They are divided into intrusive (inside Earth) and extrusive (on the surface). Examples: granite, basalt.

What are intrusive igneous rocks?
They cool slowly beneath the Earth’s surface, forming large crystals. Granite is a common example.

What are extrusive igneous rocks?
They form when lava cools rapidly on Earth’s surface, resulting in fine-grained rocks like basalt.

What are sedimentary rocks?
Formed by deposition and compression of sediments. They often contain fossils. Examples: sandstone, limestone, shale.

What are clastic sedimentary rocks?
Formed from mechanical weathering debris like sand, silt, and gravel. Sandstone is a typical clastic rock.

What are chemical sedimentary rocks?
Formed when dissolved minerals precipitate from solution. Examples: rock salt and gypsum.

What are organic sedimentary rocks?
Formed from the remains of plants and animals. Examples: coal and some types of limestone.

What are metamorphic rocks?
Formed when existing rocks are changed by heat, pressure, or chemical processes. They are denser and harder than parent rocks.

What is foliation in metamorphic rocks?
It’s the alignment of mineral grains in parallel layers due to pressure, as seen in slate or schist.

What are non-foliated metamorphic rocks?
These rocks do not show banding or layering. Example: marble, formed from limestone.

What is the rock cycle?
It explains how rocks transform from one type to another—igneous to sedimentary to metamorphic and back—through melting, erosion, pressure, and heat.

How are minerals important economically?
Minerals are vital for industries—used in construction, electronics, jewelry, agriculture, and energy production (e.g., coal, iron, copper).

What is weathering in rocks?
It’s the breakdown of rocks by physical, chemical, or biological processes, leading to soil formation and sediment generation.

What is erosion?
It’s the removal and transportation of rock materials by agents like water, wind, ice, and gravity.

What is deposition?
The laying down of sediment carried by wind, water, or ice, forming sedimentary layers that can turn into rock.

How do metamorphic rocks differ from sedimentary?
Metamorphic rocks are formed under high heat and pressure, are denser, and show recrystallization. Sedimentary rocks form from sediments and often contain fossils.

What is the difference between a rock and a mineral?
A mineral is a pure substance with a fixed formula. A rock is a mixture of minerals and has no fixed chemical composition.

What are economic minerals?
These are minerals extracted for profit due to their industrial value. Examples: bauxite (aluminum), hematite (iron), galena (lead).

What are fossil fuels?
Coal, petroleum, and natural gas are organic sedimentary resources formed from decayed plant and animal matter over millions of years.

Why is understanding rocks and minerals important?
It helps in resource exploration, construction, agriculture, and understanding Earth’s geological history and natural processes.