Science Olympiad Dynamic Planet Practice Test

Which of the following is a dark, dense, igneous rock found in oceanic crust?

1. Granite

2. Basalt

3. Limestone

4. Sandstone

The correct answer is: Basalt

The correct choice is basalt, which is a dark, dense igneous rock predominantly found in oceanic crust. Basalt forms from the rapid cooling of lava that has erupted onto the Earth’s surface or has flowed beneath the ocean. Its composition is primarily of pyroxene and plagioclase minerals, giving it a fine-grained texture. Basalt is the most common type of volcanic rock and is responsible for the formation of the ocean floor. In contrast, granite is a lighter-colored igneous rock typically found in continental crust, not oceanic. Limestone is a sedimentary rock primarily composed of calcium carbonate, and it forms in marine environments where organisms contribute to sediment accumulation, rather than from volcanic activity. Sandstone is also a sedimentary rock, characterized by its granular composition and formation from the compaction of sand-sized mineral or rock grains, and is not related to the composition of oceanic crust.