Heaviest Naturally Occurring Elements by Atomic Mass
Key Findings
About This Dataset
Heaviest Naturally Occurring Elements by Atomic MassUranium is the heaviest naturally occurring element in significant quantity, with an atomic mass near 238, followed closely by thorium (232) and protactinium (231). Every element on this list is radioactive, and most, including actinium, radium, francium, radon, astatine and polonium, exist in nature only as fleeting decay products of uranium and thorium. Their atomic masses cluster tightly between 209 and 238, reflecting how the periodic table effectively runs out of stable nuclear configurations at this end. Bismuth (209), long regarded as the heaviest stable element, is now known to be very faintly radioactive, with a half-life vastly longer than the age of the universe. Beyond uranium lie only the synthetic transuranium elements such as plutonium and americium, produced in reactors and particle accelerators rather than found in nature.
Data Insights
Numbers, trends & sources behind this chart
Methodology & source
- Data source
- IUPAC Standard Atomic Weights
- Coverage
- 10 entities · 10 observations
- Measure
- Standard Atomic Mass (u)
- Last updated
- 7 July 2026
- Compiled by
- The ANYSTAT team, from the source above
- Values are shown as reported by the source. Nothing is rescaled, rebased or converted — the only changes are thousand separators and decimals shown to two places.
- Entities are ranked highest-first on their value.
Data Sources & References
All external sources cited in this dataset
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