rocks 1

What are rocks

Naturally occurring coherent aggregates of one or more minerals accumulated as a hard substance

rocks are composed in

Lithosphere ( earth’s crust )

Characteristics of rocks

Are Composition of minerals

Are the physical mixture of one or more minerals

Take solid form due to extreme pressure

Some rocks are hard and some are soft

Wide variety of colours

Most common minerals found in rocks

Fledspar and Quartz and mica

Study of rocks ?

Petrology

Classification of rocks

1) Igneous - a) Intrusive and b) extrusive

2) Sedimentary - a) Classic and b) organic and c ) chemical

3) Metamorphic - a) Foliated and b) Non - foliated

What are primary or original rocks

Igneous rocks

Example of igneous rocks

Basalt , rhyolite , granite , diorite

Formation of igneous rocks ?

Due Cooling of magma

Which rocks are called parents of all other rocks / original or actual rock . And why ?

Igneous rocks because they comprise the earth’s crust

Most abundant type of rocks

Igneous rocks

What are the types pf igneous rocks

Intrusive igneous rocks and extrusive igneous rocks

What are intrusive igneous rocks

Formed when magma solidifies below the earth surface

Eg :- granite and dolerite

What are extrusive igneous rocks

Formed when lava solidifies above earth’s surface

Eg :- basalt and pumice

Which rocks are known as volcanic rocks

Extrusive igneous rocks

Igneous rocks based on chemical properties

Acidic igneous rocks and basic igneous rocks

What are acidic igneous rocks

Have high silica content (over 65%)

Light coloured

Eg - granite and rhyolite

Contains mainly quartz and feldspar

Found in continental crust

Their magma is viscous and leads to slow cooling and coarse grains

what are Basic igneous rocks

Have low silica content ( 45 - 55 % )

Dark coloured

Eg :- basalt and gabbro

Rich in magnesium and iron , and minerals like pyroxene and olivine

Form from fuild magma and are common in oceanic crust and volcanic areas

Process of formation of sedimentary rocks

Called Lithification ( rocks formed by successive deposition of sediments )

Sedimentary rocks are also called

Stratified rocks ( visible layers or stripes )

Which rocks or layer of rocks often contain fossils

Sedimentary rocks

Where are sedimentary rocks often found

River beds , oceans , deserts and valleys

Example of sedimentary rocks

Sandstone , limestone and shale

Classification of sedimentary rocks

Mechanically formed sedimentary rocks

Organically/ biologically formed sedimentary rocks

Chemically formed sedimentary rocks

What are mechanically formed sedimentary rocks ?

Formed by consolidation of sediments under excessive pressure and cementation

Eg :- sandstone and shale

Organically / biologically formed sedimentary rocks?

Consolidation of organic matters derived from plants and animals

Eg:- coal and chalk

What are chemically formed sedimentary rocks

Formed by chemical reaction between different compounds

Eg :- gypsum and limestone