SS 1 Second Term Agricultural Science Lesson Note – Rock Formation

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SUBJECT: AGRICULTURAL SCIENCE

CLASS: SS1

TOPIC:  ROCK FORMATION:

CONTENT:

1. Meaning/process of rock formation
2. Types of rock

Sub topic 1: Meaning /process of rock formation:

Rock is defined as any minerals materials of the earth. Rock can also be defined as the aggregates of minerals made up of hard and soft materials like stone, sands etc. Rock constitutes the significant of earth crust. The earth crust consists of rocks which is the combination of different mineral elements such as silica which contain silicon and oxygen. Rocks are aggregates (mixtures) of minerals.

ROCK FORMATION (PROCESS OF ROCK FORMATION)

Rocks are formed as a result of volcanic eruptions from earth’s crust. During the volcanic eruption the molten material or magma may remain within or escape to the surface. The magma or lava subsequently cools and solidifies to form glassy crystalline textured mass. In Nigeria rocks are found in Benue, Bauchi, Zaria, Plateau,

llorin, Ondo , Ado-Ekiti , Abakiliki and Ogoja in Cross River State , etc.

Some of the magma may cool before reaching the surface of the earth thus forming plutonic rocks (intrusive rocks) while some may {Download file to gain full access to the note}

Secondary Rock Minerals are:

(a) Oxides of metal e.g. sodium oxide (Na₂O).

(b) Mortmorilonite.

Sub topic 2: TYPES OF ROCK.

Rocks are grouped according to their mode of formation, appearance and minerals composition. Based on this analysis, there are three types of rock. They are as follows:

1. Igneous rock
2. Sedimentary rock
3. Metamorphic rock

Igneous rock:  This is formed as a result of high temperature and pressure beneath the earth’s crust which causes the liquid material (molten magma) below the earth surface to solidify or erupt in the form of a volcano. There are two types of igneous rock;

• Intrusive or plutonic
• Extrusive or volcanic

Examples of igneous rock rocks include: granite, diorite, gabbro, (they contain minerals like quart, feldspar, and mica) –plutonic,

While basalt and andesite are extrusive.

 CHARACTERISTICS OF IGNEOUS ROCK:

1 .They are coarsely crystalline in nature.

2. They are glassy in appearance.
3. They are usually hard and impervious.

SEDIMENTARY ROCK:

They are formed when weathered particles are carried from their place of origin and deposited in another area as solid particles or when the pre-existing rocks are broken down by geological denudation agents. The materials carried are usually laid down in strata/sediments/ layers. They are usually cemented together by organic matter, cemented agents or pressure.

Example of sedimentary rocks are limestone, sandstone, coal, dolomite, clay, shale, mudstone, peat, lignite, and gypsum.

Types of sedimentary rock

1.Mechanically formed sedimentary rocks

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