Mineral resources: the principal element obtained from monazite sand (common on certain coastal placer deposits) is which of the following?

Introduction / Context:
Monazite is a phosphate mineral rich in rare-earth elements and thorium. Coastal placer deposits in several countries, including India, contain monazite-bearing sands that serve as significant thorium resources, important for thorium-based fuel cycle discussions.

Given Data / Assumptions:

• We focus on the main valuable nuclear-related constituent of monazite.
• Trace or associated elements are not the target of this question.

Concept / Approach:
Monazite composition commonly includes ThO2 in appreciable amounts along with rare-earth oxides. While uranium can occur in associated minerals, thorium is the hallmark nuclear element linked to monazite, feeding thorium fuel-cycle research and policy plans in thorium-rich countries.

Step-by-Step Solution:
Identify monazite's notable nuclear element: thorium.Match to options: choose "thorium".Eliminate others that are not characteristic monazite products.

Verification / Alternative check:
Mineralogy references describe monazite as (Ce,La,Nd,Th)PO4 with variable thorium content, supporting the selection.

Why Other Options Are Wrong:

• Uranium: More associated with uraninite or carnotite, not monazite as the principal source.
• Polonium, technetium: Artificial/radioactive products, not mined directly from monazite.
• Hafnium: Typically recovered with zirconium from zircon sands, not monazite.

Common Pitfalls:
Assuming all radioactive elements are sourced from the same mineral sands; conflating zircon (ZrSiO4) with monazite-rich fractions.

Final Answer:
thorium