The hardness of various minerals on Earth was quantified as early as 300 B.C. by Theophrastus and later, in 77 A.D., by Pliny the Elder in his essay Naturalisa Historia.
Mohs scale of hardness
In 1812, the same year the United States of America declared war on England, a German geologist and mineralogist named Friedrich Mohs developed the first linear chart of hardness, now known as the Mohs scale. He devised a numerical system of one to 10, with one being the softest and 10 being the hardest:
Each mineral with a higher number must be able to scratch the one with the next lower number.
When Mohs developed his chart and up until very recently, diamonds were thought to be the hardest substance on earth. Recent discoveries of two new minerals, wurtzite boron nitrite and ionsdaleite, have displaced this notion; they have both been found to be up to 40 percent harder than diamonds. Unfortunately, neither of those two are available in sufficient quantities to conduct scientific experiments.
Revelations from Russia
Russian scientists have claimed that, during the Soviet era in the 1970s, a scientific investigation into a 60-mile-wide crater created about 35 million years ago by a giant meteor revealed an estimated trillions of carats of industrial-grade diamonds. One carat is equivalent to 200 milligrams-5 carats per gram or 141.747616 carats per ounce.
During that time, the Soviets were making good money off the production of synthetic diamonds for industrial use and, later, for jewelry. The discovery was treated as a state secret until recently. In a discussion at the Russian Academy of Sciences in Novosibirsk, they claimed the existence of this massive deposit at the Popigai Crater in eastern Siberia, which if proven, will revolutionize the industrial diamond market.
Early testing of the abundant material has shown it to be about twice as hard as currently used industrial- and jewelry-grade diamonds. This new material has been tested under extreme conditions for its pressure and temperature qualities and has been found to be superior in all aspects. These minerals have been dubbed "impact diamonds."
The head of Russia's Geological and Mineralogical Institute, Nikolai Pokhilenko, explained that the newly discovered diamonds consist of other molecular forms of carbon and could lead to an overhaul of the industrial diamond industry. To assuage the fears of the South African De Beers diamond cartel, Pokhilenko stressed that these new discoveries will not threaten the conventional jewelry diamond industry.
The Russian Academy of Sciences is planning a joint expedition to Popigai Crater with Alrosa, Russia's state-controlled mining company, after the thaw in the spring of 2013.
So, it appears that, despite the discovery of two other super-hard minerals, diamonds will continue to be known as the hardest substances on earth.
Dialing it up
As far as Mohs scale is concerned, these newly discovered treasures will have to be classified as 11, since they would be able to scratch a conventional diamond.