Most people who collect rocks have at least a basic understanding of the periodic table of the elements. (That's this table with all the element symbols and numbers like #1 - H for Hydrogen, #2 - He for Helium, etc.)
If you work your way across and down through the numbers you start to see solid metals like Carbon, Iron, Sulfur, Mercury and other important elements that are the building blocks of minerals and rocks.
We can see a mineral like Silicon Dioxide (Quartz) and we know that its made up of some kind of mixture of Silicon, and Oxygen. But have you ever wondered where that Silicon and Oxygen actually come from? The answer might surprise you.
So here's the incredible truth, lurking behind all this numbers on the periodic table of elements: (with the exception of Hydrogen, the first element); all other elements from #2 to #146, including all the elements that make up the Earth, the Moon, and all the planets from Mercury to Jupiter to Pluto, the oceans, and even the elements that make up the proteins and minerals in your body, all of these came from stars.
And perhaps even more amazing; the elements that we all love to collect in the form of rocks, (specifically, every element heavier than Iron) was created in one of the most spectacular events in the known universe - the explosion of a dying star known as a Supernova.
So, let's examine briefly how this process works- and next time you are talking rocks, you can enjoy knowing that what you are holding is quite literally - a ball of star dust.
The hydrogen fusion cycle
To understand how heavier elements and metals are formed, it important to first understand how everything, all matter, all the stuff in the universe, begins (primarily) as Hydrogen. During the big bang, most of what was ejected from that great initial explosion of matter was Hydrogen and a relatively small amount of of Helium, Lithium, Beryllium, and Boron gases. So, understanding this - it might seem strange that elements like the metal in your Pyrite or the Calcium in your Calcite, and all these other solids were made from a gas. Even Iron and Lead began as primarily Hydrogen.
At the time of the creation of the universe, as far as we understand, the universe was almost entirely hydrogen, and a menagerie of other "primordial nuclides"). And after the big bang, for millions and millions of years, that's all there was, just a huge cloud of very hot element #1 Hydrogen. But then, something strange started to happen. As the gas cooled, it also formed clumps, and the clumps became nebulae, and the nebulae, after many, many more years, became star systems.
At some point, several billion years after the big bang, these nebulae of primarily hydrogen gas, or proto-stars, started to get bigger; and in the center of these proto-stars, a miraculous thing happened. The hydrogen gas was squeezed so tightly in that center, that it began to get very hot. We know this, based on the principles of thermodynamics - the more you squeeze the same volume of gas into a smaller area, the hotter it gets.
This is increase in heat is due mostly to friction - molecules keep bumping into each other, and heating up. Well, at some point, that gas becomes very, very hot, and the pressure becomes so great, that those hydrogen molecules simply have nowhere to go... so instead of bouncing off each other, they "fuse" and 2 separate hydrogen molecules will become 1 helium molecule, releasing in the process, a whole bunch of pure energy, which we can see as light and heat.
This is where the term Nuclear fusion comes from. Because in this case, the Nucleus of two H atoms fuse together, and change to a new form. When atoms are created in this way, it is termed Nucleogenesis.
So, now we can see that what started as Hydrogen, must also contain Helium. And this is where it all begins. Stars are the "factories" that create elements; and stars of an average size can produce all elements up to, and including Iron* through Nucleogenesis, (The actual stopping point, for most stars, is the element Nickel - which then decays into Iron.) But beyond that element, it is simply not possible for typical fusion reactions to produce heavier elements. In basic terms, every time a heavier element is created, it also requires more energy, (and pressure, and heat) to get that element to undergo fusion. But not all stars, despite their awesome power and glory, have enough gas or energy to fuse heavier elements beyond a certain point. About half the remaining heavy elements are created in the processes of star death - either through the s-process which is a term for “slow neutron capture” which occurs during the death process of dwarf stars, or in the- r-process of “rapid neutron capture” which occurs during the very violent and rapid collapse of Super Giant stars, just prior to the explosion of a Supernova.
A Supernova is the explosion of certain stars. This spectacular event happen at the end of the life of very, very large stars, known as super giants. In these events, the stars experience a rapid loss of energy output, but they still have a huge amount of gasses left. As the energy needed to sustain fusion runs out, the gasses collapse inward and create one last gasp of energetic explosion that results in a vast cloud of other, heavier elements, to be formed in an instant and then violently ejected into space!
It is during this great explosion that elements heavier than those created in nucleogenesis are born, and moments later, shot at incredible speeds, in every direction. Precious metals like Gold, Silver and Platinum, exotic Rare Earth Minerals like Neodymium and Yttrium, and extraordinary radioactive materials like Uranium, all were born in these explosive events.
How heavier elements form
If you were just looking for a dinner party explanation of this process, you can probably stop here! But if you want to understand the real “nuts and bolts” of how these elements formed, you must dig deeper into the periodic table.
We have already discussed how Hydrogen can form Helium, which is the most common reaction in stars,. This process is known as the Proton-Proton Chain reaction or the p-p chain. But then this helium (actually a “heavy isotope” of helium-4) this may further form additional elements through more complex reactions like these:
In each of these fusion reactions, heavier elements are being created, which requires ever more pressure and energy to create them, and in the process, releases increasing amounts of energy. But, eventually this process simply “runs out of gas”. But the star is not really out of material - what runs out is those lighter gasses. The heavier stuff is left over, and depending on how much Hydrogen and Helium there was to start, the process might simply die off as a white dwarf star. This happens in the case of average sized stars. The amount of gas left at the end of the life of the star is not enough to cause the gravity needed to create a supernova.
We have seen what happens when you have an average size star- but if the star was very large, it will follow a different path- in this case the start will collapse in a spectacular explosion that results in a supernova, which ejects vast amounts of heavy elements in all directions, then the remaining matter will either form a super dense Neutron star, or collapse into the ultimate, most mysterious of stellar objects - a black hole.
Those heavy elements created in supergiant start, ejected during a supernova, help to seed nearby nebulae, enriching the primordial stellar matter that ultimately congeals into planetoids, asteroids, and comets that are the source of the incredible diversity of rocks and minerals we explore in this collection.
