GHS/Geography/Geography
Contents
ROCKS
DEFINITION OF A ROCK
TYPES OF ROCKS
The three main types or classes of rocks which differ because the way they are formed, these include:-
- sedimentary
Sedimentary rocks are those formed from particles(sediments) of sand, shells, pebbles, and other fragments of material. Together, all these particles are called sediment. These particles accumulate in layers and over a long period of time harden to form a rock. Sedimentary rocks are fairly soft and crumble easily.
Examples of this rock type include conglomerate and limestone.
- metamorphic
These are rocks formed under the surface of the earth from the metamorphosis (change) that occurs due to intense heat and pressure. Rocks resulting from these processes often have ribbonlike layers and can have shiny crystals, formed by minerals growing slowly over time, on their surface. examples include gneiss and marble.
- igneous
These are rocks formed when magma cools and hardens. Magma can cool inside the earth, and after some time it erupts onto the surface from volcanoes as lava. When lava cools very quickly, crystals will not be formed and the resulting rock looks shiny and glasslike. The gas bubbles are trapped in the rock during the cooling process, leaving tiny holes and spaces in the rock. Examples of this rock include basalt and obsidian.
Characteristics of different types of rocks
- small with a flat shiny surface.
- It has different imprints on the rock
- Have gas bubbles with holes.
- glassy and shiny surface.
- contain pebbles , sand and other grains visible within the rock.
- Can have straight or waves of stripes with different colors.
THE ROCK CYCLE OR HOW ROCKS CHANGE
The rock cycle starts from igneous rocks which change into sediments, sedimentary rocks later chane into metamorphic rocks, after years the rock melts and turns into magma which later comes out onto the earth's surface through volcanic eruption.
