Rocks Flashcards
Define rocks
Rocks can be defined as an aggregate of minerals that form a definite unit of the earth’s crust.
Differentiate between rocks and minerals.
- are an aggregate of minerals
are inorganic substances occurring naturally - No chemical composition
have a proper chemical composition - are divided into igneous, metamorphic and sedimentary
are divided into Silicates, sulphides, carbonates and metallic minerals. - Basalt, granite, slate, sandstone, etc
Silicon, nickel, Iron, magnesium, etc
State the 3 types of rocks
igneous, metamorphic and sedimentary
How are igneous rocks formed?
They are formed due to the solidification of magma. they are primary rocks are form the basic formation of other rocks.
Characteristics of igneous rocks.
- Hard and compact
- formed by solidification of molten magma
- They do not have layers
- Associated with volcanic activity and are hence found in volcanic regions.
- They are granular and crystaline
- The size of crystals depends on the rate of cooling.
- Rocks are less affected by chemical weathering as water doesnt enter
Different categories according to which igneous rocks are classified
- Origin
- Chemical composition
State the classification of igneous rocks based on origin.
It is divided into 2 - intrusive and extrusive
Intrusive is when the magma is cooled within the earth and under the earth’s crust. There are different types of intrusive igneous rocks.
1. Batholiths - Dome-shaped rocks with no definite floor. form the core of mountain ranges.
2. Laccoliths - Magma becomes solid right below the earth’s crust.
3. Sills - magma flows horizontally under the surface.
4. Dykes - Magma fills vertical cracks and fissures and cools.
5. Necks - magma fills an extinct volcano’s passage and solidifies.
Extrusive - when the lava cools on the earth’s surface. and it is brought to the earth by fissures and cracks.
State the classification of igneous rocks based on chemical composition.
Acid - silica content is from 65 - 85%
Ex - Quartz, Feldspar.
Basic - silica content is from 40 - 60%
Basalt, gabro
Give examples of igneous rocks.
Basalt, Gabro, Quatrz, feldspar, granite.
Why are ingenous rocks also known as plutonic rocks?
Because slow cooling causes large sized crystals to form.
what are hypobyssal rocks?
Rocks formed at an intermediate level like sills and dykes.
How are sedimentary rocks formed?
Sedimentary rocks are formed by sediments that get cemented together.
Characteristics of sedimentary rocks
- Their materials are derived from other rocks
- They have many layers
- The process of turning loose rocks into rocks is known as lithification.
- do not make massive rocks.
State the processes involved in sedimentary rocks.
- Evaporation
Water is evaporated out of the loose rocks and sediments - Compaction
Sediments are gradually sqeezed together due to piling up of layers - Cementation
bonding of the sediments by natural compounds.
Classification of sedimentary rocks on the basis of formation. state the 3 groups and their features.
Mechanically - In this process loose sediments are gradually squeezed together due to overlying layers on sediments which harden over time to form rocks.
Ex - Sandstone, Shale, etc.
Chemically - In this process mineral matter accumulates at the bottom of water bodies. The minerals are compacted to form rocks.
Ex - Rock salt, Gypsum
Organically - These rocks contain dead remains of plants and animals. They are formed from the skeletons, shells and animal remains.
Ex - Chalk.
Classification of sedimentary rocks on the basis of agents of formation.
- Riverine rocks - deposits brought by flowing water and streams
- Lacustrine rocks - bed of lakes
- Glacial rocks - debris left after glaciers melt for these rocks.
- Aeolian rocks - sand particles brought by wind.
- Marine rocks - formed on ocean floor they are of 2 types.
Calcarious - formed by shells, skeletons, etc
Carbonaceous- formed by sea plants that have remained buried for a long period of time.
what is Metamorphism??
It is the alteration of the composition or structure of the rock by heat, pressure or any other natural agent.
Characteristics of metamorphic rocks.
- Harder and more compact than original rocks
- They do not have fossils or fossil fuels inside them. Whatever is there is destroyed by heat and pressure.
- Formed due to changes in pre-existing rocks
- New minerals are formed during metamorphism
- They are impermeable and don’t allow water to percolate.
Describe the 3 types of metamorphism in detail.
- Thermal metamorphism
Transformation of the original rock takes place due to high temperature - Dynamic metamorphism
The rock’s transformation occurs due to the pressure deep within the earth’s crust. - Regional metamorphism
Igneous rocks and sedimentary rocks are buried deep under the surface. immense heat and pressure cause changes in these rocks. This is known as regional metamorphism. if it occurs over a small area it is known as local metamorphism.
State the economic importance of rocks.
- soils are derived from weathered rocks
- all types of building materials for roads, bridges, etc come from rocks.
- Are a source for precious metals
- great resource of minerals.
What is the rock cycle
The continuous process of transformation of old rocks into new rocks is known as the rock cycle.
