Maharashtra Board Class 11 Agriculture Science and Technology Chapter 1 Rock and Soil PDF Download

Rock And Soil

1.1 Definition of Rock

A rock may be defined as a hard mass of mineral matter comprising of two or more minerals. Each rock possesses certain characteristics like colour, structure, specific gravity and minerological make up.

Observe The Stones And Rocks

Collect the pieces of marble, granite, shahbadi, chalk, etc. Study their colour, hardness, granulation, etc. Match the above with different types of rocks.

Teacher's Note

You can see different rocks near your house or in your school. Try to collect small pieces and observe their colours and hardness.

Exam Trick

Remember: Rock = hard mass + two or more minerals. Think of granite from Indian temples - it has many minerals mixed together.

Points To Remember

Rock is made of two or more minerals.
Every rock has its own colour and hardness.
Rocks are found all around us in nature.
We can study rocks by collecting them from fields.

1.2 Classification Of Rocks

(A) According To Mode Of Formation

1. Igneous Rocks - These rocks were the first to be formed with the molten mass cooled and consolidated in to solid rock. They are also called as primary rocks.

These are classified as follows:

(a) The rocks formed by the slow cooling of molten magma beneath (deep) the surface is intrusive or plutonic rock e.g. Granite.

(b) The rocks formed when the magma poured out on the surface of the earth and consolidated on cooling is extrusive or volcanic rock e.g. Basalt.

Plutonic and volcanic both rocks are known as igneous or primary rocks.

2. Sedimentary Rocks - The sedimentary rocks are formed from sediments, derived from the breaking down of pre-existing rocks.

The sediments are transported by water, glaciers, etc. to new places, deposited in new arrangements and cemented to form a secondary rock.

3. Metamorphic Rocks - The igneous and sedimentary rocks undergo considerable change known as metamorphosis and the rock formed by metamorphism is known as metamorphic rock. The metamorphosis is brought about by the action of water (hydrometamorphic rock), heat (thermometamorphic rock), pressure (dynamometamophic rock) or by the combined action of all. eg: marble, limestone, etc.

Teacher's Note

Igneous rocks are formed from hot melted rock underground. You can see granite in Indian temples and basalt in the Deccan plateau.

Exam Trick

Remember: Igneous = from magma. Sedimentary = from broken rock pieces. Metamorphic = from heat and pressure changing old rocks.

Points To Remember

Igneous rocks form from cooling magma deep under ground or at surface.
Sedimentary rocks form from broken pieces of other rocks.
Metamorphic rocks form when heat and pressure change old rocks.
Rock cycle shows how rocks change from one type to another.

Teacher's Note

Different rocks have different minerals. Granite is used for making buildings and statues in India. Marble is used for making beautiful structures like the Taj Mahal.

Exam Trick

Remember the table by minerals: Granite has feldspar, Basalt is dark, Limestone has calcite. Each rock type has one main mineral you must remember.

Points To Remember

Different rocks have different minerals inside them.
Each rock has its own colour and hardness.
Rocks are found in different parts of India.
Igneous rocks are hard and strong.
Sedimentary rocks are softer and can be used as building material.

(B) Classification On The Basis Of Chemical Composition (Silica Content)

The different rocks contain silica in different proportion. On the basis of silica content they are of different types.

1.3 Definition Of Mineral

It is a naturally occurring inorganic substance having a definite chemical composition and distinct physical properties.

1.3.1 Classification Of Minerals

The minerals are classified on the basis of formation, component and specific gravity.

On the basis of formation they are:

Primary – Principal constituent of Quartz, Feldsppar, Calcite, etc.

Secondary – Deposited as a result of subsequent changes in rocks like Gypsum, Dolomite, etc.

On the basis of characteristic component they are:

Essential minerals: e.g. Feldspar, Mica, etc.

Accessory minerals: Magnetite, Tourmaline, etc.

On the basis of specific gravity they are:

Heavy minerals: e.g. Haematite, Pyrite, etc

Light minerals: e.g. Quartz, Muscovite, etc.

Teacher's Note

Minerals are natural substances with fixed chemical makeup. Quartz and feldspar are the most common minerals found in Indian rocks.

Exam Trick

Remember: Primary minerals = found first in rocks. Secondary minerals = formed later from changes. Think of primary school coming first.

Points To Remember

Minerals are natural and have fixed chemical composition.
Primary minerals are the main minerals in rocks.
Secondary minerals form from changes in primary minerals.
Heavy minerals sink in water, light minerals float.
Feldspar and quartz are the most important minerals.

1.4 Definition Of Soil

According to Jenny (1941) soil is a naturally occuring body that has evolved owing to the combined influence of climate and organisms acting on a parent material conditioned by relief over a period of time.

According to the glossary of soil science (Soil science society of Amerial 1970) the term soil is defined as

(i) The consolidated mineral material on the immediate surface of the earth that serve as a natural medium for the growth of plants.

(ii) The unconsolidated mineral matter on the surface of earth that has been subjected to an influence by genetic and environmental factor of parent material, climate (including moisture and temperature), macro and micro organisms and topography, all acting over a period of time and producing a product, that is soil. It differs from the material from which it is derived in many physical, chemical, biological and morphological chacteristics and properties.

Teacher's Note

Soil is the top layer of earth where plants grow. Good soil is very important for farming in India. Every village farmer depends on good soil for their crops.

Exam Trick

Remember: Soil = rock + water + air + dead plants. It takes many years to make soil. It is not just dirt - it is alive with many organisms.

Points To Remember

Soil is formed from broken rocks and dead plants.
Soil takes many years to form naturally.
Soil is needed for growing crops and plants.
Different soils have different colours and textures.
Soil is a valuable natural resource for farming.

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