Okay kiddo, so have you ever seen a hot spring or a volcano? Well, sometimes there are places where hot rocks deep underground heat up water, and that hot water comes out of the ground as steam. This steam can carry tiny bits of minerals with it, and if you wait long enough, those minerals might settle onto the ground around the steam vent.
These minerals that come out of the steam are called fumarole minerals. They can have pretty colors like yellow or green, and they might make the rocks around the vent look really cool and weird. So the next time you see a hot spring or a volcano, keep an eye out for fumarole minerals!