Which of the following igneous rocks can be composed of fragments?
All of these choices are correct.
Tuff
Scoria
Volcanic breccia
The correct answer and explanation is :
The correct answer is: All of these choices are correct.
Explanation (Approx. 300 words):
Igneous rocks form through the cooling and solidification of magma or lava. While many igneous rocks are crystalline, some are composed of fragments, especially those associated with volcanic activity. These are called pyroclastic rocks, formed from volcanic materials ejected during explosive eruptions.
Let’s examine each rock:
1. Tuff:
Tuff is a pyroclastic igneous rock made primarily of volcanic ash and small fragments of other rocks or crystals. These materials are blasted out during volcanic eruptions, fall to the ground, and are later compacted and cemented into rock. Tuff can be soft or hard, depending on how much it has been compacted or lithified. It clearly fits the definition of being composed of fragments.
2. Scoria:
Scoria is a vesicular volcanic rock, typically dark-colored and formed from basaltic magma. It contains numerous gas bubbles (vesicles) from volcanic gases escaping as the magma erupts. Although scoria itself is not fragmental in structure, it often breaks apart easily and can be ejected as fragments during eruptions. These solid fragments can accumulate and lithify, contributing to fragmental volcanic deposits.
3. Volcanic Breccia:
Volcanic breccia is an igneous rock composed of angular fragments of volcanic material. These fragments (called clasts) are larger than those in tuff and result from more explosive volcanic activity. The fragments may include broken lava, crystals, and ash, all welded or cemented together. Volcanic breccia is a classic example of a rock composed of volcanic fragments.
Conclusion:
Each of these rocks—tuff, scoria, and volcanic breccia—can form from volcanic fragments in different ways, making the statement “All of these choices are correct” the best answer. These rocks highlight the diversity of processes involved in volcanic eruptions and igneous rock formation.
