The chemical element of atomic number 90, a white radioactive metal of the actinide series. (Symbol: Th)
- In addition to primeval heat, Earth's core also gets heat from radioactive decay of uranium, thorium, and potassium.
- All natural rocks contain small amounts of uranium and thorium, which are radioactive and remain so for billions of years.
- The analysis shows that manganese, titanium, hafnium, thorium, phosphorus, and the rare-earth elements play a significant role in discriminating between zircons of various origins.
Mid 19th century: named after the god Thor.
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