Quartzite is an extremely hard rock formed when sandstone is transformed by intense heat and pressure deep underground. Imagine squeezing a sandcastle so hard that the individual grains fuse together into solid stone: that's essentially what happens to create quartzite, though it takes a very long time and temperatures that are extremely hot.

Quartzite ranks among the hardest rocks on Earth, which makes it incredibly durable. Ancient peoples used quartzite to make tools and weapons because it could hold a sharp edge better than most other stones. Today, builders prize quartzite for countertops, floors, and outdoor features that need to withstand heavy use and harsh weather. A quartzite countertop can last for decades without scratching or wearing down.

The rock often appears in shades of white, gray, or pink, though mineral impurities can create striking patterns of red, yellow, or even purple. Geologists love finding quartzite because it tells them that an area once experienced tremendous geological forces: the rock's very existence proves that ancient mountains were built, continents collided, or Earth's crust buckled and folded under immense pressure.