Naturally radioactive minerals are not very radioactive!
This is because they are formed from naturally occurring radioactive isotopes
which, by necessity, have extremely long lifetimes - comparable or greater than
the age of the Earth itself. The radioactivity of an isotope is strongly
dependent upon its half-life. Tritium (hydrogen-3) has a half-life of only 11.2
years, meaning that half of it decays every 11 years. It is highly radioactive -
but not nearly as radioactive as some isotopes used in medicine, such as
Technetium-99 with a half-life of only 6 hours. A unit of Technetium-99 emits
16,000 times as much radiation per second than does Tritium, which in turn is
7,000,000 times as radioactive as Plutonium!
There are no plutonium minerals. Consider Plutonium-244 (the most stable
isotope of plutonium). It has a half-life of 82 million years - and consequently
is not very radioactive. Yet in the 4.5 billion year existence of the Earth, the
total number of remaining atoms dropped in half 550 times. There simply is none
left to form minerals.
There are four main radioactive isotopes that have lasted as long as the
- Uranium-239 (over 99% of all uranium) with a half-life of 4.5 billion
- Uranium-235 (less than 1% of all uranium) with a half-life of 700
- Thorium-232 (100% of Thorium) with a half-life of 14 billion years
- Potassium-40 (0.01% of all potassium) with a half-life of 1.28 billion
years. Since there is so little of this isotope compared to stable
Potassium-39 and 41, potassium minerals are not considered radioactive
(although they all are, to a tiny degree).
That means that essentially all radioactive minerals contain either uranium
or thorium. The Rare Earth Elements typically include a percentage of uranium
and/or thorium as trace elements, rendering many of them slightly radioactive.
Note that both uranium and thorium have decay chains involving many short-lived
isotopes (they consequently emit much more radiation than a simple isotope such
as tritium), but these are present in tiny traces and typically don't exist long
enough to become concentrated and form minerals.
There are other relatively common radioactive nuclides: Radium-226 and
Radon-222 are both produced during the decay of Uranium. Radon is considered the
most hazardous, because as a gas we breathe it into our lungs where it can
attach until it decays. Luckily, Radon only has a 4-day half-life, which limits
the build-up in a basement or from a concrete wall. Unluckily, Radon only has a
4-day half-life, which means it is extremely radioactive.
Another well-known radioactive isotope is Carbon-14, produced as a measurable
trace by cosmic rays acting on atmospheric CO2, and with a half-life of 5732
years. Since it is carbon, it is readily incorporated into all living things.
Indeed, our bodies are naturally radioactive, to a degree, from all of these
sources (Potassium-40 contributes the most, then Carbon-14, then Uranium and its
Minerals containing Thorium (including two minerals also containing
Minerals containing Uranium (radioactivity is proportional to the
fraction of uranium, and alpha particles are primarily emitted from the
Rare Earth Oxides (REOs)
and Trash Can Minerals (which tend to concentrate the leftovers after
common minerals have formed, and will generally include traces of Uranium and/or
Thorium: "traces" means they are less radioactive):
Note that my statement that Uranium and Thorium are not very
radioactive does NOT mean they aren't dangerous! There are different
types of ionizing radiation with different hazards. Beta radiation (high-energy
electrons), Gamma rays (high-energy photons), Neutrons, and Alpha particles
(high-energy helium nuclei) have different effects and respond differently to
shielding. The primary type of radiation emitted by Uranium and Thorium is in
the form of alpha particles which are extremely potent but easily shielded.
Placing a specimen beneath a glass or plastic dome will block more than 99% of
the radiation. Even a sheet of paper will block it, or the outer (dead) layers
of your skin. The danger from alpha-emitters is in breathing dust (or gas such
as Radon), which places radioactive particles in contact with live tissue which
is easily damaged by the radiation.
For safety, ALWAYS keep radioactive minerals in a display case and/or
dome, MINIMIZE handling which can release dust particles, IMMEDIATELY WASH hands
and clothing that comes into contact with radioactive minerals, HOLD YOUR BREATH
while handling specimens (or opening containers which might retain radon), and
VACUUM or WASH to clean - do not blow dust off. All of these precautions are
intended to prevent inhaling (or eating) radioactive particles. Again, simply
touching a uranium or thorium mineral with your hand is not intrinsically
Don't worry about sending trash to an incinerator, as they release far more
radiation into the air than from other materials than from the dust in your
packaging! In fact, many times more radiation has been released into the
environment in the form of uranium as a trace component of coal ash than from
nuclear power plants; the ash is not very radioactive, but there is a lot of it
(especially from older power plants), and while the waste from a nuclear power
plant is extremely radioactive (due to the fission products of uranium and/or
plutonium atoms), it is well monitored. After all, the workers in a nuclear
power plant are worried about radiation and work hard to keep it contained, but
not the workers in a coal-burning power plant.
Technical Crystal Habits
Descriptive Crystal Habits
Index of Refraction
Reaction to acids