[Rockhounds] What Is The Hardest Substance In The Universe?

[Kreigh Tomaszewski]

If asked to name the hardest thing in the universe some might suggest that
subject they failed in second year or making a Flat Earther acknowledge
reality
<https://www.iflscience.com/how-to-talk-to-a-conspiracy-theorist-65766>.
Specifying that we mean the hardest substance would probably lead to most
people saying diamonds, but as with so many questions
<https://www.iflscience.com/what-is-the-heaviest-object-in-the-universe-68995>
 in this series
<https://www.iflscience.com/what-is-the-fastest-solid-object-we-know-68537>,
the answer isn’t quite as straightforward as your memory banks may tell
you.

For centuries, diamonds were the epitome, and indeed the definition of a
hard material. Now, it’s arguable they have been surpassed, but the story
is not simple.

In 1812 Friedrich Mohs wanted to create a scale of the hardness of
substances. Mohs lacked a way of measuring the extent to which substances
deform under pressure, so he used talc as his starting point, defining it
at one. He set diamonds, the hardest mineral he knew, at 10, leaving
everything else to be intermediary between the two. Hardness was assessed
based on the capacity of one material to create a visible scratch on the
other, such as the famous (but unreliable) testing if a claimed gemstone
<https://www.iflscience.com/if-you-find-a-precious-gemstone-can-you-keep-it-67541>
is
real by seeing if it could scratch glass.

Moh’s scale has its problems, including the fact that the values he
assigned to intermediary substances were not linear. Nevertheless, it is
still in use today for some purposes. Field geologists find it useful in
identifying unknown rocks without access to testing equipment.

As a result of the weaknesses in the Mohs’s scale, other measures of
hardness have been introduced with more numerical rigor. For example, the
Vickers hardness scale measures the load a substance can resist without
deforming.

Initially, however, irrespective of the scale used, diamonds remained the
hardest substance. Indeed, the Vickers test is conducted by applying great
force to a pyramid-shaped diamond pressed against the substance being
tested. The four carbon bonds, uninterrupted by the impurities of other
gemstones, were tough to beat, and it was widely assumed nothing could be
harder.

https://www.iflscience.com/what-is-the-hardest-substance-in-the-universe-71226