Mohs hardness — material just below diamond: Which material ranks immediately below diamond on the Mohs hardness scale?

Introduction / Context:
The Mohs hardness scale ranks minerals by scratch resistance from talc (1) to diamond (10). It is widely referenced in materials selection, abrasives, and wear assessment, even though it is an ordinal, not linear, scale.

Given Data / Assumptions:

• Standard Mohs reference minerals: corundum is 9, topaz is 8, calcite is 3.
• Diamond is 10.
• Silicon carbide is a manufactured abrasive with hardness comparable to ~9–9.5 on various scales, but Mohs standard mineral 9 is corundum.

Concept / Approach:
In the classic Mohs sequence used for education and field testing, the mineral ranked just under diamond is corundum (Al2O3). While modern abrasives like silicon carbide and boron carbide can be extremely hard, the Mohs reference immediately below 10 is corundum at 9.

Step-by-Step Solution:
List Mohs references: 8 = topaz, 9 = corundum, 10 = diamond.Compare options: corundum matches the rank directly below diamond.Select corundum as the correct answer.

Verification / Alternative check:
Mineralogy tables and materials handbooks confirm corundum as Mohs 9 and the standard just below diamond.

Why Other Options Are Wrong:
Topaz: Mohs 8, two steps below diamond. Silicon carbide: very hard abrasive, but the Mohs canonical mineral at 9 is corundum. Calcite: soft mineral at 3.

Common Pitfalls:
Equating engineered abrasive hardness scales with the Mohs ordinal mineral list; they are related but not identical.

Final Answer:
Corundum (aluminium oxide)