Calcareous sinter

Calcareous sinter is a type of rock that is formed by the things that live in water. When we look in a glass of water, we might see little particles floating around. Those particles can be things like tiny bits of dirt or even little animals and plants too small for us to see! These little animals and plants are called "microorganisms."

When these microorganisms live in water that has a lot of calcium in it, they can build up little homes for themselves. Think of building blocks that they put together to create a little house or a castle. These "building blocks" are made from the calcium in the water. Over time, these little homes can build up layer upon layer, creating a type of rock called calcareous sinter.

So, just like how we can build towers out of blocks or Legos, these microorganisms build up layers of calcium to make their own homes. And when we see the result, we call it calcareous sinter!