Question

Name the following rocks: 1\. An extrusive rock with 40% Ca-rich plagioclase and 60% pyroxene 2\. An intrusive rock with 65% plagioclase, 25% amphibole, and 10% pyroxene 3\. An intrusive rock with 25% quartz, 20% orthoclase, 50% feldspar, and minor amounts of biotit

Short answer

The rocks are named as follows: 1. Basalt (extrusive rock with 40% Ca-rich plagioclase and 60% pyroxene) 2. Diorite (intrusive rock with 65% plagioclase, 25% amphibole, and 10% pyroxene) 3. Granite (intrusive rock with 25% quartz, 20% orthoclase, 50% feldspar, and minor amounts of biotite)

Step-by-step solution

Identify the type of rock and mineral composition for the first rock

We are given an extrusive rock with 40% Ca-rich plagioclase and 60% pyroxene minerals present.

Identify the first rock

Given that it is an extrusive rock with significant proportions of Ca-rich plagioclase and pyroxene, we identify this rock as Basalt.

Identify the type of rock and mineral composition for the second rock

We are given an intrusive rock with 65% plagioclase, 25% amphibole, and 10% pyroxene minerals present.

Identify the second rock

Given that it is an intrusive rock with a majority of plagioclase along with amphibole and pyroxene, we identify this rock as Diorite.

Identify the type of rock and mineral composition for the third rock

We are given an intrusive rock with 25% quartz, 20% orthoclase, 50% feldspar, and a minor amount of biotite minerals present.

Identify the third rock

Given that it is an intrusive rock with a majority of quartz, orthoclase, and feldspar minerals, and a minor amount of biotite, we identify this rock as Granite. So, the rocks are named as follows: 1. Basalt 2. Diorite 3. Granite

Key concepts

Extrusive Igneous Rocks

Extrusive igneous rocks form when magma reaches the Earth's surface and cools rapidly. This rapid cooling process doesn't allow for large crystals to form, often resulting in rocks with fine-grained or glassy textures.

Common examples of extrusive igneous rocks include basalt and obsidian. Basalt, which composes much of the oceanic crust, is known for its dark color and small crystal sizes. It forms from the rapid cooling of low-viscosity lava that is rich in magnesium and iron.

A closer look at the mineral composition reveals that basalt often contains Ca-rich plagioclase and pyroxene, which are the minerals that give basalt its characteristically dark color and dense structure. The understanding of basalt’s mineralogy aids in its identification in field studies and laboratory analyses.

Intrusive Igneous Rocks

In contrast to extrusive rocks, intrusive igneous rocks form from magma that cools slowly beneath the Earth's surface, allowing time for large crystals to grow. This results in a coarse-grained texture.

Diorite and granite are two key examples of intrusive rocks. Diorite is composed mainly of plagioclase along with smaller amounts of pyroxene and amphibole, giving it a mixed light and dark appearance. On the other hand, granite is lighter in color, typically consisting of quartz, orthoclase, and feldspar with minor amounts of mica like biotite.

Understanding these mineral compositions and their percentages helps geologists to classify and name intrusive rocks. For students, recognizing the crystal size and mineral content is essential in rock identification exercises.

Mineral Composition

Mineral composition is a defining characteristic when it comes to identifying and classifying rocks. Each rock has a unique combination of minerals, which can be identified by their specific properties such as color, hardness, crystal shape, and cleavage.

For igneous rocks, the mineral composition reflects the conditions under which the rock formed. For instance, a high percentage of plagioclase and pyroxene suggests a mafic composition common in basalt, while a composition rich in quartz and orthoclase points to a felsic rock like granite. It's essential to be able to quantify these minerals, as their relative percentages provide clues about the rock's origin and environment of formation.

Geology Education

Geology education encompasses the study of the Earth, its materials, the processes that act upon them, and its past. Through the study of geology, students learn about igneous, sedimentary, and metamorphic rocks and the rock cycle that interlinks them.

Identifying rocks is a crucial skill for students in geology education, which is honed through the examination of mineral content, texture, and formation processes. Engaging in activities such as rock identification exercises helps students develop observational and analytical skills crucial for their future careers in geosciences.

Furthermore, understanding geology is not only academic but also has practical applications in environmental protection, natural disaster management, and resource extraction, thus making geology education important for a broad range of societal issues.