Volcano Rock Assignment Example | Topics and Well Written Essays - 750 words

Volcano Rock - Assignment Example Because of their less density magma usually moves upwards. Of in any case they make it to the surface they usually crystalize leading to the formation of volcanic rocks.The naming of volcanic rocks is usually one in accordance to their chemical composition. Because of the difference in the rate at which magma solidifies there is always a difference in the rate at which they solidify. Volcanic rocks usually have two main categories namely: extrusive volcanic rocks and intrusive volcanic rocks. Extrusive volcanic rocks are those that come into existence as a result of eruption of seafloor fissures and volcanoes. They are also sometimes as a result of freezing in the shallow depths. This implies that extrusive volcanic rocks cool at a high rate under relatively low pressure. This can be used as an explanation for them being glassy and fine grained. Intrusive volcanic rocks on the other side take a little longer to solidify and do not produce gasses (Erickson and Muller 212). Due to the high rate of cooling at the surface the resulting rocks usually have many tiny crystals which lead to the aphanitic texture of extrusive volcanic rocks. Magma that slowly cools at the depth leads to the formation of few but large crystals which result to the phaneritic texture of intrusive volcanic rocks. However, there is always a different texture formation in cases when the magma starts by cooling slowly then starts cooling faster later (Zhang 253). The resulting texture is always referred to as porphyritic texture. The composition of magma is always determined by the abundance of elements that are in the earth. Some of the elements that are usually among the composition of magma include silicon, aluminum, calcium, magnesium, sodium, potassium, hydrogen, and oxygen. These elements make 99.9% of the elements that are found in the earth. Because of the abundance of oxygen the chemical analysis of volcanic rocks is always done in terms of oxides of the