What is the most durable rock on earth?

Without a doubt, the title holder for “World’s Toughest Rock” (not a mineral, but a rock) has to go to Banded Iron Formation, or at least to a related variety of ironstone (there are several).

Anyone who’s ever dealt with Banded Iron Formation, which we usually refer to as BIF, knows that it’s a beautiful rock that is also an absolutely gnarly bitch to break or cut. The reason is pretty simple: it is composed of alternating layers (bands) of quartz, which is already a pretty hard material, and hematite. Hematite is Fe2O3. It is hard. It is iron. It is not your…