Igneous Rocks MCQ Quiz: Trivia!

Igneous rock originates when hot, molten material called magma cools and crystallizes. Magma is a molten mixture of minerals and gases that is found beneath the Earth's surface. As magma cools, it solidifies and forms igneous rock. This process can occur either beneath the Earth's surface, resulting in intrusive igneous rocks, or on the Earth's surface, resulting in extrusive igneous rocks.

An intrusive rock is formed below the earth's surface through the process of solidification of magma. These rocks are characterized by their coarse-grained texture due to slow cooling and crystallization. They often have a visible interlocking structure of minerals. Therefore, the correct answer is "Intrusive" as it describes the formation of rocks below the earth's surface.

Extrusive rocks are formed from volcanic activity at the Earth's surface. When magma erupts onto the surface, it cools quickly and solidifies, forming fine-grained rocks such as basalt or rhyolite. In contrast, intrusive rocks, such as laccoliths, dikes, batholiths, and sills, are formed from magma that cools slowly beneath the Earth's surface. Therefore, the correct answer is extrusive, indicating that the rock is formed at the Earth's surface.

In a rock with a porphyritic texture, the large crystals are referred to as phenocrysts. Porphyritic texture is characterized by the presence of both large and small crystals in the rock. The large crystals, known as phenocrysts, are surrounded by finer-grained crystals called groundmass. Therefore, phenocrysts is the correct term to describe the large crystals in a rock with porphyritic texture.

Igneous rocks rich in dark silicate minerals with about 50 percent silica are said to have a basaltic composition. Basaltic composition refers to rocks that are rich in iron and magnesium, and have a lower silica content. These rocks are typically dark in color and have a fine-grained texture. Basaltic composition is commonly found in volcanic rocks, such as basalt, which are formed from the rapid cooling of lava on the Earth's surface.

Igneous rocks that form from the last minerals to crystallize from magma will have a granitic (felsic) composition consisting of quartz, potassium feldspar, and sodium-rich plagioclase feldspar. This is because granitic rocks are typically light-colored and rich in silica, which is represented by the presence of quartz. Additionally, potassium feldspar and sodium-rich plagioclase feldspar are common minerals found in granitic rocks. The term "felsic" refers to rocks that are rich in feldspar and silica, which is characteristic of granitic compositions.

A pluton is a large igneous rock body formed by the solidification of magma beneath the Earth's surface. It is typically composed of granite or other intrusive igneous rocks. Plutons are formed when magma cools and crystallizes slowly over a long period of time, allowing the minerals to grow and form a solid rock mass. They are often found in mountainous regions and can range in size from a few meters to several kilometers in diameter. Plutons are important in geology as they provide valuable insights into the Earth's history and the processes that occur beneath the surface.

Erosion is the process in which the earth is worn away. It involves the removal and transportation of soil, rock, or sediment by wind, water, or ice. This process can occur naturally over time due to weathering and natural forces, or it can be accelerated by human activities such as deforestation or construction. Additionally, erosion plays a role in the creation of rocks through the deposition and compaction of sediment over time. Therefore, the correct answer is "Both" as erosion involves both the wearing away of the earth and the creation of rocks.

A laccolith is a type of igneous rock formation that occurs when slow-moving magma is injected into the Earth's crust and forms a mushroom-shaped body. The magma solidifies underground and creates a dome-shaped structure with a flat base. This process is known as intrusive igneous activity because the rock is formed beneath the Earth's surface.

The correct answer is "Intrusion of magma into fractions." This refers to the process in which magma, or molten rock, is injected into pre-existing rock formations, causing them to fracture and allowing the magma to fill the cracks. This can lead to the formation of intrusive igneous rocks, such as granite, as the magma cools and solidifies within the fractures.