Based on Mohs hardness, which of the following materials is the hardest: calcite, quartz, corundum, or gypsum?

Introduction / Context:
Hardness influences wear, grinding energy, and equipment selection. Mohs scale provides a simple ranking used in mineral processing and materials engineering.

Given Data / Assumptions:

• Compare typical Mohs values.
• Materials: gypsum 2, calcite 3, quartz 7, corundum 9.

Concept / Approach:
Corundum (aluminum oxide) at Mohs 9 is harder than quartz (7), calcite (3), and gypsum (2). Harder materials raise liner wear and energy needs during grinding.

Step-by-Step Solution:
Recall Mohs ranking.Pick the maximum value.Select corundum.

Verification / Alternative check:
Reference charts list corundum just below diamond (10).

Why Other Options Are Wrong:
Gypsum/Calcite: much softer.Quartz: hard but below corundum.

Common Pitfalls:
Confusing corundum with quartz due to both being common abrasives.

Final Answer:
Corundum