"Diamonds are made deep underground when the carbon is subject to high
pressure and heat. Is there any way that other elements could be used to
make an even harder type of diamond? I was thinking if the elements were
present in similar conditions on other planets where the pressures would be
greater (due to the planet being more massive). Of course us finding them
would be really difficult."
Hannah - So, diamonds from the ancient Greek, meaning unbreakable. They're formed naturally around the earth’s centre where the high pressure and temperatures cause bonding between electrons of carbon atoms. This gives rise to the rigid lattice crystal carbon structure of diamond, which then travels to the earth’s surface during volcanic eruptions, delivering us with the transparent, extremely hard material we know as diamond. But could other planets produce similar substances? For the answer, we turn to Director of Research and Development at Deep Space Industry’s Dr. Stephen Covey.
Stephen - You might expect that silicon, just below carbon in the periodic table and also with 4 bonding electrons would form equivalent structures. But silicon atoms are much larger than carbon atoms and don’t pack as closely and this form softer molecules.
Nitrogen has a smaller covalent radius than carbon and under super high pressures, over a million atmospheres, solid nitrogen changes from a hexagonal lattice into a cubic lattice, similar to diamond, and might have similar or even greater hardness. But it’s difficult to beat diamond as a hard mineral. This is due to the way the carbon atoms are linked together, resulting in the highest packing density of any known substance at room temperature and pressure.
But there may indeed be other ultra hard materials formed at extremely high pressures. In February of 2009, a paper in Physical Review Letters reported that worksite structured boron nitride may be 18% harder than diamond and then another carbon mineral, lonsdaleite is 58% harder than diamond. In January of 2013, the journal Nature reported the production of ultra-hard nanotwinned cubic boron nitride by researchers from the University of Chicago, which also appeared to be harder than diamond.
So, if the conditions are right then harder minerals than diamond may indeed be formed in the depths of large planets. Whether or not they are stable enough to be brought to the surface without reverting to softer forms, is another question altogether.