How Do Extrusive Igneous Rocks Form? скачать в хорошем качестве

How Do Extrusive Igneous Rocks Form?

Extrusive rocks are igneous rocks that are formed when molten rock (magma) cools and solidifies. These rocks are referred to as extrusive as they are formed at the Earth's surface. The entire cycle of magma production is the same as the formation of intrusive rocks.. They only vary in where the cooling of molten rock took place. So, as this magma continues to rise, it pushes against the solid crust, and a reservoir of liquid rock, called a magma chamber, forms. Some of the magma may feed the volcanoes on the Earth's surface, but most remains trapped below. As the temperature continues to drop, the magma starts cooling and crystallizing. If such a process continues over millions of years, it will solidify the magma, turning it into intrusive rocks. While this process continues, the gas molecules in the magma begin to bubble out of the solution. It rises and expands, causing fractures in the surrounding rock. These cracks, called 'vents,' are what allow the magma to reach the surface, resulting in a volcanic eruption. The ejected magma, now called lava, remains molten and flows across the ground until it cools and solidifies into rock. Because it has been exposed to a cooler air temperature, it hardens instantly, depriving the mineral crystals of a chance to grow. Thus, the rocks that form have a very fine-grained or even glassy texture that requires magnification in order to see the invisible crystals. So, these rocks that form from lava and solidify quickly on the Earth's surface are known as extrusive igneous rocks.