Geology
All about rocks
By: Ana Meulenberg
Types of rocks
There are only 3 types of rocks. They are: Igneous, Metamorphic and Sedimentary rocks.
Igneous
Igneous rocks are formed when magma or lava cools down. Igneous rocks are identified by the holes or bubbles in them.
Basalt
Basalt is a dark, finely grained stone. It is mostly made up of Plagioclase and Pyroxene. This specimen is about 5 centimetres.
Obsidian
Obsidian is a volcanic glass that forms from the very fast cooling of molten rock material. It cools so fast that no crystals form.
Diorite
Diorite is an intrusive igneous rock that contains a mixture of Feldspar, Pyroxene, Hornblende and occasionally Quartz.
Sedimentary
Sedimentary rocks are formed when the elements wear rocks down into tiny particles of dust, sand and soil. After a while they are cemented together and hardened. Sedimentary rocks are identified by the different color grains and layers.
Rock Salt
Rock Salt forms from the evaporation of ocean or saline lake waters. It is found in areas of very arid climate. This rock is about 5 centimetres in length.
Sandstone
Sandstone is made up of sand-size weathering debris. Sandstone always has visible multi-coloured grains. This specimen is 5 centimetres across.
Conglomerate
Conglomerate has round particles inside it. The round particles are more than 2 millimeters in diameter. Around the particles it is filled with chemical cement. This rock is about 2 centimetres long.
Metamorphic
Metamorphic rocks are formed when igneous or sedimentary rocks change after being exposed to extreme heat or pressure without melting. Metamorphic rocks usually have shiny crystals in them.
Gneiss
Gneiss is a rock that is made of granular mineral grains. It contains abundant Quartz or feldspar minerals. Gneiss has bands of different colours.
The Gneiss picture above is about 5 centimetres in length.
Marble
Marble is produced from the metamorphism of limestone. It is mostly made up of Calcium Carbonate. This marble rock is about 5 centimetres across.
Amphibolite
Amphibolite forms through recrystallization under conditions of high viscosity and directed pressure.
This specimen of rock above is also 5 centimetres in width.
The rock cycle
What would happen to a rock over a million years?
Rocks from mountains get weathered and eroded and then the broken rocks in a form of dust will eventually get carried by a river into the ocean. It then sinks to the bottom and it compacts forming a sedimentary rock. Then when the temperature changes and rises the minerals inside the rock start to change. This new rock is now a metamorphic rock. This cycle can go on for so many millions of years. So I think that over a million years this rock may go through this cycle hundreds of times.
Interesting facts about rocks
Did you know?
That Basalt is the most common rock found on earth
The layers on Sedimentary rocks are arranged according to their density
A rock that you pick up from anywhere could have already been millions of years old and gone through all the transformations
There are over 700 different types of Igneous rocks identified
That Basalt is the most common rock found on earth
The layers on Sedimentary rocks are arranged according to their density
A rock that you pick up from anywhere could have already been millions of years old and gone through all the transformations
There are over 700 different types of Igneous rocks identified
Metamorphic rocks are called so, because they always start off as another rock
95% of the Earth's crust is made of Igneous rock
The Rock Cycle
Igneous rocks
Classified by their bubbles and holes
Sedimentary
Classified by the different coloured layers of grains
Metamorphic
Classified by crystals
Rocks Types & Rocks Cycle - Video for Kids by makemegenius.com