RocksGroup1

Rocks: A naturally occuring solid aggregate of minerals.

There are three types of rocks; Igneous, Sedimentary, Metamorphic. The way a rock is classified is determined by the way it was formed.



IGNEOUS ROCKS - Defenition - one of the rock types. Formed by magma ( molten rock ) being cooled and solidified. They may for with or without crystallization. Either below the surface ( intrusive* ) rocks or outside the earth surface ( extrusive **) outside the earth
 * inside the earth**

Classified is several ways, and methods of classification have evolved a lot over the past 100 years. Each classification is useful for a certain purpose and reflect a particular way of looking at igneous rocks.
 * How Igneous Rocks are classified:

Color and Texture : There are several classification techniques to classifying igneous rocks that apply different methods and derive different results. One technique applies chemical composition as the major distinguishing factor. This technique provides the petrologist (or rock scientist) with a good objective method of determining the true origins of the rock from a plate tectonics aspect. The chemistry of igneous rocks and plate tectonics are closely related and therefore the origin of a rock's chemistry and not its minerals or methods of formation is important to petrologists who use this method of classification. Another classification technique uses the mineral components of the rock and is called the modal method of classification. Identification of the rock's minerals is of course important and is easy to do when the minerals are found in large crystals and can easily be identified. This method has "official" approval and is generally what petrologists use to classify rock samples. A third general type of classification uses a variety of characteristics and is therefore more subjective, but sometimes easier to use for the average rock hound. It involves the use of the rocks texture, color and mineralogy.

Mafic- relating to a group of dark-colored minerals, composed mostly of magnesium and iron, that occur in igneous rocks. Felsic- relating to a group of light-colored minerals, composed mostly of magnesium and iron, that occur in igneous rocks.**

METAMORPHIC ROCKS-** metamorphic rocks are one major group that makes up the crust of the Earth; consists of pre-exisiting rock mass in which new minerals or textures are formed at higher tempature and greater pressures than those present on the Earth's surface.

Those are some examples of Metamorphic rock.

They are formed by the alteration of pre-existing rocks from exposure to heat and pressure while remaining in a solid form. Metamorphism* occurs by breaking bonds between atoms in a mineral so that the atoms rearrange themselves into new, more stable, mineral forms. Rocks are transformed and remain in a solid state because not all the bonds in the rock's minerals are broken - if they were the rock would melt. Metamorphism occurs in solid rock because only some of the bonds between atoms are broken in an unsecure mineral form. As a result, the freed atoms and ions can move to another location within the mineral, or bond with atoms in a different mineral. The end result is to produce minerals that are more secure under the environmental conditions in which they exist.


 * The process by which rocks are changed into other forms by the application of heat and/or pressure.

SEDIMENTRY ROCKS- one of the major groups of rock that makes up the crust of the Earth; formed by the deposition of either the weather remains of other rocks, the results of biological activity, or precipitation from solution.



Sedimentary rocks are classified by Clastic* or Non Clastic. An example of sedimentary rocks are coal,sandstone,conglomorate and limestone.
 * Made up of pre-existing rocks.