ROCKS
Rocks are aggregates of minerals which differ from one another in texture, structure, colour, permeability, mode of formation and degree of resistance to denudation.
FEATURES OF ROCKS
Hardness: refers to the strength of a rock i.e. its resistance to weathering and erosion
Permeability: ability of water to pass through rocks
Porous: rocks that allow water to pass through pores
Pervious: rocks that allow water to pass through joints and bedding planes
Joints: these are vertical cracks in rocks
Faults: fractures running through rocks caused by tectonic movements
Fold: buckled or bent layers of rocks caused by tectonic movements
Bedding planes: horizontal cracks between layers in sedimentary rocks.
TYPES OF ROCKS
Rocks are grouped into 3:
1. IGNEOUS ROCKS
2. SEDIMENTARY ROCKS
3. METAMORPHIC ROCKS
IGNEOUS ROCKS are rocks that result from volcanic activity
CHARACTERISTICS:
Crystalline in nature
Do not occur in layers
No fossils
Usually hard and impervious
Resistant to erosion
TYPES OF IGNEOUS ROCKS
Plutonic/ Intrusive igneous rocks: are formed at some depth in the earth crust; magma cools and slowly solidifies beneath the earth surface, forming large crystals e.g. granite, gabbo and diorite
Volcanic/ Extrusive igneous rocks: are formed from molten rocks poured out of volcanoes as lavas. These molten rocks cool and solidify rapidly on the earth surface, forming small crystals e.g. basalt
* Magma – molten rocks from volcanoes
SEDIMENTARY ROCKS are formed from sediments deposited either by water, wind, or ice.
CHARACTERISTICS:
Occur in layers
Coarse, fine, soft or hard
Non-crystalline
Contain fossils of plant and animals
Not resistant to erosion
TYPES OF SEDIMENTARY ROCKS
1. Mechanically formed sedimentary rocks
2. Organically formed sedimentary rocks
3. Chemically formed sedimentary rocks
METAMORPHIC ROCKS (Changed rocks) Formed from...