Types Of Rocks And How They Form

Are you looking to know the types of rocks and how they form? Then, the following information is for you. There are three major classes or types of rocks: igneous, metamorphic, and sedimentary rock. The difference among these classes of rocks is based on how they are formed.

Types of rocks and how they form – Sedimentary Rock

This type of rock is created from pebbles, shells, sand particles, and other material fragments. These particles together form what is known as sedimentary rock. These particles slowly build-up over an extended period of time and becomes hard, forming a rock in the process. Sedimentary rocks are formed when dissolved minerals are crystallized. The particles accumulate for thousands or even millions of years before they form layers of the hard substance known as sedimentary rock. This type of rock is usually soft and might crumble or break easily. When you look at a sedimentary rock closely, you will often see pebbles, sand, and other particles. Also, they are the only types of rock that contain fossils. Limestone and conglomerate are two good examples of these types of rock.

Types of rocks and how they form – Metamorphic Rock

These types of rock are usually formed from the intense heat and pressure that occur under the earth’s surface. The process of forming the rock is what is referred to as metamorphosis. The rocks formed from the metamorphosis of the earth’s surface often have shiny surfaces and have layers like ribbons. Some very good examples of metamorphic rocks include marble and gneiss.

Types of rocks and how they form – Igneous Rock

These are mainly formed after the cooling and hardening of magma (molten rock). At some times, it stems from volcanoes, which is known as lava. But at other times, it results from the cooling of magma beneath the earth’s surface. When lava quickly cools down, there are no crystals formed and the rock looks glasslike and shiny.

At times, bubbles of gas become entrapped during the rock’s cooling process, leaving spaces and tiny holes in the rock.

They vary in grain size, permeability, texture, color, and composition. At the eruption of volcano, it results to molten rock which is ejected into the surface of the earth. Then the molten rock (magma) cools and solidifies, resulting to a mineral crystal known as igneous rock. The size of igneous rock after formation largely depends on the length of time it takes the magma to cool (the shorter the time the smaller the crystal formed).

The igneous rock is composed of mineral crystals and becomes fine grained or coarse grained, which largely depends on the level of cooling. Granite is a very good example of an igneous rock that is coarse-grained. Other compositions of igneous rock include mica, feldspar, and quartz. The quartz has a glassy and grayish appearance, while the mica is shiny and black and lesser in quantity than feldspar and quartz.

Types of rocks and how they form – Basalt

The basalt is a good example of an igneous rock with tiny pores (fine-grained). They are made of feldspar and a very good proportion of dark colored minerals like pyroxene and olivine. The above are the major types of rocks and how they form. So, all rocks in the earth’s surface fall under these categories.