Correct option is C
Introduction
Radioactive minerals contain unstable isotopes of uranium or thorium that emit ionising radiation as they decay.
Several rare-earth and phosphate minerals carry these elements within their crystal lattice, making them naturally radioactive.
Information Booster
The intended answer is — Allanite, Monazite, and Autunite.
A. Allanite is a complex calcium–rare-earth aluminium–iron silicate that typically contains radioactive thorium and uranium, and some allanite transforms into less crystalline metamict allanite during alteration as thorium and uranium leach out. Its radioactivity is a recognised field indicator.
B. Monazite is a rare-earth phosphate that is a classic radioactive/thorium-bearing mineral.
It contains 5–12% (typically about 7%) thorium, and is a major source of thorium from beach-sand (monazite placer) deposits, highly relevant to India's coastal thorium reserves.
E. Autunite is a uranium mineral — a radioactive mineral whose uranium in its chemical formula Ca(UO₂)₂(PO₄)₂·10–12H₂O provides its radioactivity, and it is one of the most popular uranium minerals among collectors.
Additional knowledge
C. Sillimanite — Correctly excluded. Sillimanite is an aluminosilicate (Al₂SiO₅) refractory mineral containing no uranium or thorium; it is entirely non-radioactive and is used industrially in high-temperature ceramics.
· D. Xenotime — Here is the important caveat: xenotime is actually a radioactive mineral. It is an yttrium phosphate with traces of uranium and thorium, appears in the standard list of radioactive minerals, and is mined alongside monazite.
English
10 Questions
20 Marks
12 Mins
