AN INTRODUCTION TO ROCKS.
There are three main different types of rocks: igneous, sedimentary and metamorphic. Below are descriptions and examples of each.
IGNEOUS ROCKS:
Igneous rocks are the oldest type of rock and is a volcanic rock. It comes from deep in the earth where magma is formed. When the magma reaches the earths surface and turns into lava, it cools and turns into igneous rock. This type of rock may have crystals, air bubbles or a glassy surface. They can appear to be glassy and dense.
EXAMPLES OF IGNEOUS ROCKS:
Below are three common examples of Igneous rocks:
ABOVE: Andesite.
ABOVE: Obsidian
ABOVE: Basalt
SEDIMENTARY ROCKS:
Sedimentary rocks are often formed from mud or sand settling at the bottom of a body of water. This kind of rock may contain fossils, have wavy horizontal lines, visible grains, layers and can be dusty. Sedimentary comes from when rock is subjected to weathering and is transported into a body of water, where it eventually makes it's way down and is buried, where it is pushed lower and lower, and gets hotter and hotter, before turning into another kind of rock.
EXAMPLES OF SEDIMENTARY ROCKS:
Below are three examples of Sedimentary rocks:
ABOVE: Sandstone
ABOVE: Shale
ABOVE: Breccia
METAMORPHIC ROCKS:
Metamorphic rocks are a changed kind of rock. This change they go through is caused by heat and pressure, sometimes splitting them into many layers, with different mineral grains throughout the rock. Metamorphic rocks are formed when sedimentary rocks are buried down underneath the earth's surface, where they are under an immense amount of heat and squashing.
EXAMPLES OF METAMORPHIC ROCKS:
Below are some examples of Metamorphic rocks:
ABOVE: Quartzite
ABOVE: Marble
ABOVE: Slate.
THE ROCK CYCLE:
The rock cycle is the never-ending process that rocks pass through as they change type over and over as they are subjected to heat, pressure, weathering and erosion, which causes the developments. The rock cycle is how rocks develop their identifying characteristics such as crystals, grains and the type they are. The rock cycle takes many, many, many years, and below is a description of how it works:
DESCRIPTION OF THE ROCK CYCLE:
All rocks start life deep down in the depths of the earth as magma. Molten rock is pushed through the upper mantle and the mantle to reach the core, and then forms either extrusive or intrusive igneous rock when it reaches the crust. The extrusive igneous rock exits through an eruption out of a volcano as lava, cooling and turning into rocks with small crystals. The intrusive igneous rock crystalizes over a long period of time and very slowly is pressured up to the surface.
From there, the rock is weathered and eroded over a long period of time, (remember, the whole rock cycle itself takes a very, very, VERY long time, as does each stage!) and eventually is transported into water, where it breaks down into sediment.
The sediment is subjected to burial and compaction and eventually is buried down to become sedimentary rock. From there, it can either be subjected to pressured and pushed upward to the surface, or can be affected by immense pressure and heat and becomes Metamorphic rock.
Once it has become Metamorphic rock, it can either be pushed up to the surface or melted, to begin the cycle all over again.
From there, the rock is weathered and eroded over a long period of time, (remember, the whole rock cycle itself takes a very, very, VERY long time, as does each stage!) and eventually is transported into water, where it breaks down into sediment.
The sediment is subjected to burial and compaction and eventually is buried down to become sedimentary rock. From there, it can either be subjected to pressured and pushed upward to the surface, or can be affected by immense pressure and heat and becomes Metamorphic rock.
Once it has become Metamorphic rock, it can either be pushed up to the surface or melted, to begin the cycle all over again.