Radioactive
All Rocks Are Radioactive (and So Are All Bananas), but Meteorites Are Less Radioactive Than Earth Rocks, on Average
Three chemical elements are naturally radioactive and occur in all Earth rocks and all meteorites – K (potassium), Th (thorium), and U (uranium). Any rock from any planet will contain at least one atom of these elements so, technically, all rocks are radioactive, it is just a matter of degree. On average, however, meteorites are considerably less radioactive that typical Earth rocks.
Concentrations of Radioactive Elements in Meteorites, Earth Rocks, Bananas, and People
| Substance | K (ppm) | Th (ppb) | U (ppb) | |
| 1 | Ordinary Chondrites (88% of all stony meteorites) |
780–825 | 42–43 | 12–13 |
| 2 | Sayh al Uhaymir 169 (the most radioactive meteorite) |
4400 | 31,000 | 8000 |
| 3 | Earth’s Continental Crust (range of 4 estimates) |
9000–26,000 | 3500–7200 | 900–1800 |
| 4 | Meteorwrongs (mean of 598 samples) |
10,200 | 6300 | 2500 |
| 5 | Terrestrial Granite (range of 18 diverse samples) |
23,000–57,000 | 1500–130,000 | 800–63,000 |
| 6 | My Kitchen Countertop (garnetiferous leucogranite) |
47,700 | 16,200 | 2100 |
| 7 | A Banana (a good source of potassium!) |
3800 | ?, but low | ?, but low |
| 8 | Human Being | 2000–3000 | ~1 | ~1 |
| ppm = parts-per-million (μg/g), ppb = parts/billion (ng/g) |
| 1. Ordinary Chondrites data from Wasson J. T. and Kallemeyn G. W. (1988) Compositions of chondrites, Philosophical Transactions of the Royal Society of London A, v. 325, p. 535-544. |
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2. SaU 169 data from Korotev R. L, Zeigler R. A., Jolliff B. L., Irving A. J., and Bunch T. E. (2009) Compositional and lithological diversity among brecciated lunar meteorites of intermediate iron composition. Meteoritics & Planetary Science, v. 44, p. 1287-1322. Dr. Hofmann told me that SaU 169 did, in fact, register as radioactive with a laboratory survey meter (below). |
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3. Earth’s Continental Crust data from Weaver B. L. and Tarney J. (1984) Physics and Chemistry of the Earth (Pollack H. N. and Murthy V. R., eds.), v 15, Pergamon, Oxford, p. 39-68. Taylor S. R. and McClennan S. M. (1985) The Continental Crust: Its Origin and Evolution, Blackwell Sci. Publ., Oxford, p. 312. Wedepohl K. H. (1995) Geochimica Cosmomochimica Acta v. 59, p. 1217-1232. |
| 4. Terrestrial Granite data from Govindaraju K. (1994) 1994 compilation of working values and sample description for 383 geostandards. Geostandards Newsletter, v. 18, p. 1–158. |
| 5. My Kitchen Countertop data from my laboratory |
| 6. Meteorwrongs. I encourage people to obtain a chemical analysis of their rock if they really want to know if it is a meteorite. This row contains average concentrations for 598 rocks for which people have sent me the data and there were data for all 3 elements. Five of the 598 “meteorwrongs” were, in fact, meteorites – 4 ordinary chondrites and 1 iron. |
| 7. Banana data from https://www.chiquita.com/fruits/bananas-class-extra/ |
| 8. Human Being data from several internet sources. |
