Radioactivity is a fascinating natural physical phenomenon, discovered at the beginning of the twentieth century by French scientists Henri Becquerel and Pierre and Marie Curie – all three Nobel Prize laureates. The phenomenon is characterized by the disintegration of unstable atoms, called radioisotopes. The result is the release of energy and matter in the form of different rays that are, depending on the case, called ɑ, β or γ rays. These atoms are thus transformed into more or less stable atoms that have lost a part of their mass and that can also continue to disintegrate.

All the rocks and minerals on Earth that contain atoms of uranium, thorium, and to a lesser degree potassium, are radioactive, because uranium and thorium slowly change into lead, and potassium into argon, while emitting radiation.

As uranium and thorium exist in only small concentrations in the Earth’s crust and as potassium is a lot less radioactive (though much more abundant), the radioactivity emitted by rocks and minerals is not dangerous. It doesn’t begin to become so unless the uranium and thorium are concentrated, which is what is done in the civil and military nuclear industries.

The 80% of the Earth’s internal heat at the root of its tectonic activity – earthquakes, volcanoes, continental drift, the forming of mountains and valleys – is due to the radioactivity of the three elements above. (We can also include poor evacuation of heat, as rocks are excellent thermal insulators.) The remaining 20% comes from the residual heat left over from the Earth’s creation. Even if uranium and thorium exist in low concentrations and potassium is only slightly radioactive, the accumulation of their radioactivity inside the globe produces a colossal amount of heat that keeps the inside of our planet hot and allows for tectonic activity. The solid crust on which we live floats and slides on a soft substratum, much like a raft on water.

And so, the great variety of landscapes and life forms on Earth probably wouldn’t exist as we know them without the radioactivity of these three atoms and the heat that they generate. Contrary to Earth, other heavenly bodies like the Moon are too small to keep enough of this heat of radioactive origin: their volume, in which this heat was produced, is too small compared to their surface where this heat is dissipated. Thus, their appearance has not changed in billions of years, whereas the Earth’s face continues to evolve.

The collection presents a series of high-level radioactive specimens – mainly phosphates/vanadates/arsenates, silicates and oxides that have been regrouped outside of their usual corresponding classes. Even if their radioactivity is without danger – after all, they are natural rocks – it is nonetheless slightly higher than average for rocks. And so we prefer to exhibit them in secured display cases in a special room: The walls carry a protective layer of lead that reduces the transmission of radiation and entry into the room is through a baffle to prevent this radiation from leaking out into the main room. Finally, the display cases are equipped with vents that suck up the radon gas generated by radioactivity and release it outside the building, where it is dispersed in the air in harmless quantities.

Aside from oxides, which are generally black – the uraninite exhibited being among the best specimens known for this species – silicates and phosphates/vanadates/arsenates display a variety of colors in bright green, orange or yellow hues. An interesting fact: some Native American tribes reduced these minerals into powders to make body paint!