It's possible that Bort's actual gemstone is carbonado. Bort tends to be a common lower grade diamond (and slightly less hard than regular diamonds), while carbonados are one of the toughest diamond variety. Carbonado is also used in cutting tools, but is a polycrystalline diamond made of three allotropes of carbon: diamond, graphite, and amorphous carbon. Rather than a solid specimen, carbonado is made up of smaller specimens and have much of the properties similar to Bort's. Scientists haven't figured out how carbonado is made on earth, and some theories suggest that it's extraterrestrial.