Rocks That Get Formed by Lava

Igneous Rocks

• Igneous rocks form when lava erupts and comes out of the surface of the Earth. Igneous rock is formed when the lava or magma from a volcano cools and solidifies. Igneous rock may or may not have crystallization. There are two classifications of igneous, including intrusive igneous and extrusive igneous rocks.

Composition of the Lava

• Most igneous rocks are divided into three classifications --- felsic, intermediate, and mafic --- based on the chemical composition of the lava. If the lava was superheated, there is a fourth classification known as ultramafic.

  Felsic lava has a high viscosity and strength. Felsic lava is composed of aluminum, calcium, potassium, silica, sodium, feldspar and quarts. Felsic magma erupts at lower temperatures, ranging from 650 to 750 degrees Celsius.

  Intermediate lava has a lower composition of aluminum and silica and is normally richer in magnesium and iron than felsic lava. The lava is normally hotter as well, ranging from 750 o 950 degrees Celsius. Intermediate lava has a lower viscosity than Felsic lava.

  Mafic lava, also known as basaltic lava, erupts at temperatures over 950 degrees Celsius and contain a higher level of iron and magnesium than Felsic and Intermediate Lava. This lava normally has a low viscosity.

  Ultramafic lava contains high levels of magnesium and is erupts at temperatures over 1,200 degrees Celsius. Ultramafic lava has a viscosity similar to that of water.

Intrusive Igneous

• Intrusive igneous rocks form when magma cools and solidifies within the Earth's crust. Intrusive igneous rocks is surrounded by rock that existed before the volcano erupted. Intrusive igneous rocks have a coarse texture and include granite.

Extrusive Igneous Rocks

• Extrusive igneous rocks form at the surface of the crust and cooled more quickly than intrusive igneous rocks. Since extrusive igneous rocks cooled more quickly they are fine grained and softer. Examples of extrusive igneous rock includes obsidian and pumice. Obsidian is produced when felsic lava erupts and cools rapidly with a low amount of crystallization. Pumice is highly porous and is often formed when lava and water mix together, causing depressurization.