Igneous Rocks Formed Directly From Magma

Running Head: VOLCANIC ROCKS 1
VOLCANIC ROCKS 3

Volcanic Rocks Student’s Name Institution’s Name

Volcanic Rocks.
Igneous rocks are found abundantly in the earth’s crust. Two processes lead to the formation of Igneous rocks. The first process results when the molten or liquid rock(magma) cools and crystallizes deep inside the earth thus forming the characteristic rocks. They can also be formed when the molten rock(lava) erupts from a volcano and hardens or crystallizes on the surface of the earth. These two processes lead to the formation of two separately characterized rocks from the same original substance. These variations include physical characteristics like the texture and the color which helps in identifying them (Lutgens et al., 2008.)
Grain size or texture is used to differentiate the two basic types of volcanic rocks. Texture reveals the size of the crystals and thus shows where the rock was formed. It explores the origin of the rocks. Another parameter it shows is dependent on how fast they cooled. Also, the texture can reveal the amount of gas that was trapped within the magma during the rock formation(Jerram & Petford, 2013). Important to note is that texture does not tell how the rock feels. Rocks with coarse texture or large crystals reveal that the rock cooled slowly inside the earth (intrusive rocks). Examples are granite and diorite which are used as building material (Lutgens et al., 2008.)
The other type of volcanic rock has fine texture (minuscule crystals). Their crystals are so because of the rapid cooling of lava on the earth’s surface. Because of this cooling on the land’s surface, they are known as extrusive or volcanic rocks. They may be vesicular during their formation (have trapped air.) examples are pumice, used in making lightweight concrete, and obsidian, employed in ornaments (Lutgens et al., 2008.)

Reference:
Lutgens, F. K., Tarbuck, E. J., & Tasa, D. (2008). Foundations of earth science. Upper Saddle River, NJ: Pearson Prentice Hall.
Jerram, D., & Petford, N. (2013). The field description of igneous rocks. Hoboken, N.J: Wiley.