I was just about to mention thorium separately, in reply to gumby's comment above about the size of the subcontinent and its mineral potential, then saw your comment mentioning thorium, and decided to piggyback on it:
I have read somewhere that the black sands of Kerala's coast are black due to thorium. I have read that more than once, in different places.
[ Monazite is an important ore for thorium,[8] lanthanum, and cerium.[9] It is often found in placer deposits. India, Madagascar, and South Africa have large deposits of monazite sands. The deposits in India are particularly rich in monazite.
Monazite is radioactive due to the presence of thorium and, less commonly, uranium. ]
