Engineering geology — properties of quartzite (a metamorphic rock) Which set of descriptors best matches quartzite, a metamorphic stone derived from sandstone?

Introduction / Context:
Quartzite is a metamorphic rock formed when quartz-rich sandstone is subjected to heat and pressure, causing recrystallization and interlocking of quartz grains. Understanding its mechanical and physical properties is critical for its use in construction, flooring, and as aggregate.

Given Data / Assumptions:

• Parent rock: sandstone composed predominantly of quartz.
• Metamorphism leads to interlocking crystalline texture.
• Typical engineering descriptors: hardness, brittleness, compactness.

Concept / Approach:
During metamorphism, silica cements and quartz grains fuse, producing a dense, crystalline mass with high hardness (quartz hardness ~7 on Mohs scale). The strong interlocking texture makes quartzite hard and compact, but like many strong rocks, it tends to fail with limited plastic deformation, so it is described as brittle under load.

Step-by-Step Solution:
Identify mineralogy: largely quartz → high hardness.Identify texture: recrystallized, interlocking grains → crystalline and compact.Relate mechanics: strong and stiff but with limited ductility → brittle behavior.Therefore, all descriptors (hard, brittle, crystalline, compact) apply.

Verification / Alternative check:
Hand specimens show sugary to glassy luster and conchoidal fracture; density and rebound hammer readings reflect compactness and hardness.

Why Other Options Are Wrong:
Any single descriptor alone is incomplete; quartzite typically exhibits all listed properties, hence “All of the above” is correct.

Common Pitfalls:
Confusing quartzite with quartz-rich sandstone (less compact, clastic); misidentifying foliated metamorphic rocks (e.g., schist) as quartzite; assuming hardness implies toughness (brittle rocks can chip under impact).

Final Answer:
All of the above