Which mineral exhibits a conchoidal fracture?
Quartz
Halite
Gypsum
Calcite
The Correct Answer and Explanation is :
The correct answer is Quartz.
Explanation:
Quartz, a common mineral made of silicon dioxide (SiO₂), is known for its conchoidal fracture. A conchoidal fracture refers to the way some materials break along smooth, curved surfaces, often resembling the ripples of a seashell. This type of fracture is typically seen in minerals or materials that lack cleavage planes, meaning they do not break along predictable lines. Quartz is one of these minerals.
Quartz is hard (ranking 7 on the Mohs hardness scale), and its atomic structure does not allow it to cleave cleanly along flat surfaces. Instead, when force is applied, quartz breaks irregularly, resulting in a smooth, curved surface. This is what gives it the conchoidal fracture appearance. These fractures can vary in size from small, shallow curves to large, sweeping ones, depending on the nature of the break.
Other minerals in the list, like Halite (NaCl), Gypsum (CaSO₄·2H₂O), and Calcite (CaCO₃), have distinct cleavage planes, meaning they break along specific, flat surfaces. For example:
- Halite has cubic cleavage, breaking into cubes due to the arrangement of its crystal structure.
- Gypsum exhibits good cleavage in one direction and poor cleavage in two others.
- Calcite has rhombohedral cleavage, breaking along three planes that form rhomboid shapes.
These cleavage characteristics make the breakage patterns of halite, gypsum, and calcite predictable and different from the conchoidal fracture found in quartz. This difference between cleavage and conchoidal fracture helps geologists and mineralogists identify minerals in the field. Quartz’s conchoidal fracture is one of its most distinctive physical properties, used to differentiate it from minerals with similar appearances.