A bornhardt is a big rock that sticks up out of the ground like a giant's tooth. Think of it like a mountain, but instead of being tall and pointy, it's more like a huge rock that's flat on top. These rocks are really hard and sturdy, so over time, erosion from things like wind, rain, and ice wear away the weaker rock around it but leave the bornhardt standing proud. You might even see them in the desert, where there's not a lot of vegetation to cover them up. It's like a huge, natural sculpture made of super-strong stone!