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Let’s start off with the rock cycle

Current theory states that the earth has an inner core and an outer core. On top of the outer core is the biggest area called the mantle. The last layer is the atmosphere. The lithosphere, or crust, is broken up into plates called tectonic plates. Some of the plates spread apart from each other, and some of the mantle comes up into the lithosphere, hardens, and forms new crust. Some of the plates come together and parts of the plates are subducted back into the mantle.

This forming of new crust and destruction of old crust is what powers the rock cycle, and creates the first type of rocks: igneous.

Igneous

Newly formed rocks are called igneous rocks. Igneous means “it came from fire.” Igneous rocks are formed by cooling magma, or lava, which comes from the mantle of the earth.

Rocks are classified by their origin or how they are formed.

There are two kinds of igneous rocks. Some of the rocks are formed and cooled under the earth. Others are formed on top of the earth and in contact with air.

Little by little, over thousands or millions of years, sediments collect layer-by-layer, forming thick deposits on land or on the sea floor. These layers are pressed down more and more through time, until the bottom layers slowly turn into rock. This process is known as lithification (lithos being the Greek word for “stone”). A unique feature about sedimentary rocks is the fact that they tend to be laid down in layers, known as strata. Examples of sedimentary rocks are: sandstone, gypsum, limestone, shale, and conglomerate. The scientific study of these rocks assists humans in the quest to know more about the earth’s history, and about the naturally processes which have shaped the earth.

Igneous rocks are formed when volcanoes erupt, causing the magma to rise above the earth’s surface. When magma appears above the earth, it is called lava. Igneous rocks are formed as the lava cools above ground. They are also formed when the melted rock, (called magma), becomes trapped deep within the earth in small pockets. As these pockets of magma cool, they become igneous rocks. The solidification process is very complex. There are different ranges of melting temperatures for the magma. The minerals with the highest melting points will crystallize first and their crystal growth continue as long as the surrounding material remains molten. Depending upon the surroundings and the rate of cooling, a great variety of igneous rocks can be formed. When crystallization is complete, the result is a solid mass of interlocking crystals of different sizes. The most abundant types of igneous rocks are granite and basalt.

The original rock does not melt. The elements in the minerals can actually form new minerals. The new rocks that develop are called metamorphic rock.

Because they are on the crust, they cool quickly and are fine-grained. Crystals haven’t had time to form. Basalt is formed by the extrusive process.

Intrusive rocks cool below the surface, inside of the earth’s crust. Since they’re not exposed to air, they cool much slower than extrusive rocks. This slow cooling time gives crystals time to form and intrusive rocks have a coarser grain.

If you concluded that this information is worthwhile you might also wish to be more topics about Sedimentary Rocks Pictures and also Obsidian Rocks.