There’s no single hardest rock on Earth. The strongest types, on the other hand, include quartz in their makeup: quartzite, quartz sandstones, rhyolites and granites, according to the MadSci Network. While many cite diamonds as the hardest rock on Earth, this is incorrect.
Reference: www.reference.com/science/hardest-rock-earth-402c36f284c19e4c
Is diamond the strongest metal on Earth?
Still, however it is crafted, the combination of steel with other strong metals makes it the strongest known metal in the universe. As for hardness, chromium is the hardest known metal. While the hardest known mineral in the universe is diamond, the honor of the hardest metal goes to chromium.