Igneous Rocks Essay Example

without volcanic eruption. Over thousands of years, the magma hardens to form intrusive rocks.

Intrusive rocks have visible crystals because they cool slowly. These rocks can be categorized as felsic, intermediate, mafic, or ultramafic. Felsic rocks, high in silica, are usually light-colored. Granite is an example of a felsic intrusive rock.

The text provides information about various types of rocks and their characteristics. It explains that felsic rocks are light in color and have a high silica content, while intermediate rocks are darker in color and have lower silica content compared to felsic rocks. An example of an intrusive intermediate rock is diorite. Conversely, mafic rocks have low silica content and contain magnesium and iron. Gabbro is given as an example of an intrusive mafic rock. Ultramafic rocks have very low silica content and typically appear dark due to their abundance of magnesium. Peridotite serves as an example of an intrusive ultramafic rock. The text then transitions to discussing faults and folds, defining a fault as a fracture occurring within the earth's crust.

Faults in the earth, also referred to as fractures, come in different types: dip-slip and strike-slip. Dip-slip faults are characterized by slip parallel to the fault's dip, while strike-slip faults consist mainly of horizontal sections. An example of a strike-slip fault is the San Andreas Fault found in California.

Some faults are categorized from different viewpoints, such as normal, reverse, thrust, and strike-up faults. A normal fault occurs when the rock above the fault surface moves downward in relation to the block below it. Conversely, a reverse fault involves the upward movement and displacement of the block above the fault surface over the lower block.

Thrust faults,

considered reverse faults, have a shallow dip angle. On the other hand, strike slip faults involve mostly parallel and horizontal movements along the fault's strike. Geologically speaking, a fold refers to a bend or deformation in stratified rocks resembling a wave. Certain folds are categorized as sedimentary rocks.

A fold is composed of three elements: two bends and one limb. The two outside ends are the limbs, while the middle section acts as the limb. Folds are tectonic structures or processes that bend in two opposite directions. They can be found in various orientations, such as upward, downward, curved, or inclined.

The text describes different types of folds and their classifications. An arch is an upward fold called an anticline, while a depression is a downward fold. A monocline is a steep fold that moves in one direction. Folds can be classified as vertical, inclined, or nonplunging and are commonly found in folded regions and cratons. Large folds occur along the edges of synclines and areas of the cratons. These folds can impact the distribution of facies, the thickness of sedimentary strata, and the accumulation of sediments in plate tectonics.

The presence of folds is sometimes connected to petroleum deposits. To identify extrusive and intrusive rocks, refer to the table below, which includes pictures. Select at least two intrusive rocks and two extrusive rocks and insert a picture of each rock in the Picture column. Provide a description of the physical characteristics for each rock and write a 50- to 100-word explanation concerning how these characteristics demonstrate whether it is an extrusive or intrusive rock.