Question

Which rock has large mineral grains? A) granite C) obsidian B) basalt D) pumice

Short answer

Granite has large mineral grains.

Step-by-step solution

Understand the Structure of Rocks

Rocks can be classified based on their grain size and how they form. Granite, basalt, pumice, and obsidian each have different characteristics. Recognizing these differences is key to identifying the rock with large mineral grains.

Analyze Granite

Granite is a coarse-grained igneous rock. It forms deep beneath Earth's surface, allowing large crystals to grow, which makes its mineral grains visible to the naked eye.

Analyze Obsidian

Obsidian is an igneous rock that cools so quickly that crystals do not have time to form. This results in a glassy and smooth texture, with no visible grains.

Analyze Basalt

Basalt is a fine-grained igneous rock that cools quickly on the Earth's surface. Its mineral grains are very small and usually not visible without a microscope.

Analyze Pumice

Pumice forms from volcanic explosions and has a frothy texture full of air bubbles. It is a light rock with very tiny mineral grains, often not visible to the naked eye.

Determine the Rock with Large Mineral Grains

Based on the analysis, granite is the rock with large mineral grains compared to the other options. Its slow cooling process allows substantial crystal growth.

Key concepts

Igneous Rocks

Igneous rocks are fascinating geological formations that arise from the cooling and solidification of magma or lava. They are broadly classified into two main types based on their formation location:

• Intrusive Igneous Rocks: These form from magma that cools slowly beneath the Earth's surface. The slow cooling process allows the formation of large, visible mineral grains. Granite is a prime example of this type.
• Extrusive Igneous Rocks: These rocks form from lava that cools rapidly on the Earth's surface. This quick cooling results in smaller grains that are not easily visible. Examples include basalt, pumice, and obsidian.

Identifying igneous rocks involves examining their grain size and texture, which are indicative of their cooling history and the environment where they formed.

Mineral Grains

Mineral grains in rocks are the crystals that become visible when you closely examine the rock's surface. The size of these grains helps us understand the history of how the rock formed. Here are some key points about mineral grains:

• Size: Large mineral grains generally form because the rock has cooled slowly, giving crystals more time to grow. Small grains, by contrast, suggest rapid cooling.
• Visibility: Large grains are visible to the naked eye, whereas small grains might require a microscope.
• Arrangement: The way grains are arranged and interlock can tell us about the rock's history and its formation processes.

Understanding mineral grains is crucial in rock identification because they provide insights into the environment and conditions under which the rock was created.

Granite Characteristics

Granite is a well-known rock in the field of geology, renowned for its large mineral grains and appealing appearance. Here are some defining characteristics:

• Coarse-Grained Texture: Granite features large, visible crystals that form due to the slow cooling of magma beneath the Earth's surface.
• Mineral Composition: It is composed mainly of quartz, feldspar, and mica, contributing to a range of colors from pink to gray.
• Durability: The interlocking crystal structure makes it a very strong and durable rock, ideal for construction and decoration.
• Geological Significance: Because of its large grains and varied mineral composition, granite is often studied to understand Earth's geological history.

Its unique characteristics make granite an essential rock for both scientific studies and practical applications. Granite's mineral grains make it distinctive among igneous rocks.