Metamorphic, Sedimentary and Igneous Rocks

Sedimentary

Sedimentary rocks are formed when intense pressure is applied to rock particles that have been deposited together from air, water and ice. As the rock deposits build up, the particles turn into layered solids because of the intense pressure on the rock which makes the liquid in the rock push itself out. The liquid is found in the rocks pores because of the deposition and the fact that the sediments were probably laying in the bottom of a lake. This process is known as lithification and happens over a long period time. Sediments are mud, sand and pebbles. They create sediment deposits by building up in the bottom of lakes and rivers. The pressure on top of the lower level of sediment begins to compress the sediments to stone pushing out the water in the sediments.

Some sedimentary rocks contain fossils because the way the sedimentary rocks are formed does not hurt the plant or animal remnants. Sedimentary rocks cover 75% of the earths surface but it is only 5 percent of the earths interior. This means that the other 95% belong to the metamorphic and igneous rock formations.

Sedimentary rocks that consist of limestone, sandstone, shale, clay and chalk are important to our society because they are great building materials. Hydrocarbons can be found in sedimentary reservoirs because the sedimentary rocks often form loose reservoirs in sedimentary basins which, in some cases, allows the hydrocarbon to sit amongst the loose rocks.

Metamorphic

MMetamorphic rocks are created from intense heat and pressure being applied to an existing rock. The existing rock is called the protolith. The protolith could be an older metamorphic rock, igneous rock or sedimentary rock and has to be subjected to intense pressure and heat over 150 degrees Celsius in order to change the rocks chemical makeup or physical appearance. Metamorphic rocks are developed deep down in the earth and are classified by their texture and their chemical and mineral makeup. They can also be formed from lava being poured over the top of the earth's surface, where rocks lay underneath. Metamorphic rocks form the greatest this way when there is direct contact between the lava and the rocks. There is also great height and pressure on the rocks from the lava which is why they form the best with direct contact. Metamorphic rocks make up a large part of our earths crust. Studying metamorphic rocks has taught us a lot about the heat, pressure and depth of the earth.

Igneous

Igneous rocks are formed when lava cools. The lava can cool under the ground which is called intrusive or it can cool above the ground which is called extrusive. This cooling process forms intrusive or extrusive igneous rocks. The magma is formed from melted rocks at the earths surface or in the earths centre. The melting of the rocks can be caused from an increase in temperature, a change in composition or a decrease in temperature. Igneous rocks can be classified by how they were made, their texture, mineralogy, chemical composition and the location of the igneous body. There are over 700 known igneous rocks and the majority of them have been formed under the earths surface. Igneous rocks make up for 95% of the earths crust but is covered by a thin layer of sedimentary rocks. Igneous rocks are important to scientists because there mineral and chemical makeup tell us what they earths centre is made of. They allow us to make a time sequence of events since the rocks true date can be figured out by radiometric dating. Igneous rocks also allow us to do tectonic reconstitution because there features are usually characteristic specific to a tectonic region and in some cases they contain important minerals like ore. The word igneous in Latin means fire.

 

-------------------

     Bibliography

Wikipedia. “Igneous rocks” September 16 2006; September 17 2006.
(http://en.wikipedia.org/wiki/Igneous_rocks)
 
Wikipedia. “Metamorphic rocks” September 13 2006; September 17 2006.
(http://en.wikipedia.org/wiki/Metamorphic_rocks)
 
Wikipedia. “Sedimentary rocks” September 14 2006; September 17 2006.
(http://en.wikipedia.org/wiki/Sedimentary)
 
Qin. “Sedimentary Rocks Formation” 1997; September 17 2006.
(http://www.geocities.com/RainForest/Canopy/1080/sedimentary_formation.htm)
 

This article was written by Jenny Hanna, 2006.