How are igneous rocks form
Igneous rocks are formed through the process of solidification and crystallization of molten magma or lava. The word "igneous" comes from the Latin word "ignis," meaning fire. To understand how igneous rocks are formed, let's break down the process step-by-step:
1. Magma Formation: Magma is a molten mixture of various elements and compounds, including silicate minerals, found beneath the Earth's surface. It is formed by the melting of pre-existing rocks due to increased temperature and/or decreased pressure. Magma can also be generated during volcanic activity when solid rock melts in the Earth's mantle or crust.
2. Intrusive Igneous Rocks: When magma rises and cools slowly beneath the Earth's surface, it solidifies and forms intrusive igneous rocks. The cooling process is much slower due to the insulating effect of the surrounding rock, resulting in the growth of large mineral crystals. Examples of intrusive igneous rocks include granite and diorite.
3. Extrusive Igneous Rocks: When magma reaches the Earth's surface through volcanic eruptions or fissures, it is then called lava. Upon exposure to the atmosphere, lava cools rapidly and solidifies, forming extrusive igneous rocks. The cooling process is quicker compared to intrusive rocks, leading to the formation of smaller mineral crystals or even glassy textures. Examples of extrusive igneous rocks include basalt and pumice.
In summary, igneous rocks are formed through the solidification and cooling of molten magma below or above the Earth's surface. The rate of cooling, presence of pressure, and the mineral composition of the magma all influence the size and texture of the resulting igneous rocks.