Michigan Test for Teacher Certification (MTTC) Secondary Integrated Science Practice test

How are rocks primarily classified?

1. By their size and color

2. Based on chemical composition and formation methods

3. According to their mineral content only

4. By their age and geographic location

The correct answer is: Based on chemical composition and formation methods

Rocks are primarily classified based on their chemical composition and the methods by which they were formed. This classification system divides rocks into three main types: igneous, sedimentary, and metamorphic. Igneous rocks are created from the solidification of molten material, either magma beneath the Earth's surface or lava that has erupted. Sedimentary rocks form from the accumulation and lithification of sediment, which can include mineral fragments and organic material. Metamorphic rocks arise from the alteration of existing rocks through pressure, heat, and chemically active fluids. While size, color, mineral content, age, and geographic location can provide additional context or detail about rocks, they do not form the primary basis for classification in the geological sense. The focus on how rocks are formed and what they are made of provides a more systematic and scientifically valid way to categorize the vast variety of rocks found in nature.