Here's how it works:

* Dissolution: Rainwater absorbs carbon dioxide from the atmosphere, forming a weak carbonic acid. This acidic water seeps into the ground and dissolves limestone (which is primarily composed of calcium carbonate).

* Formation of Caverns: Over time, this process creates large underground cavities known as caverns.

* Speleothems: As the acidic water drips from the ceiling or seeps from the walls, it releases carbon dioxide and deposits calcium carbonate. These deposits form the beautiful formations we see in caves, such as:

* Stalactites: Hang from the ceiling, looking like icicles.

* Stalagmites: Rise from the floor, often forming directly below stalactites.

* Columns: When stalactites and stalagmites meet.

* Flowstone: Forms along the walls and floors of the cave in sheets.

So, the characteristic formations in underground caverns are made from the same mineral that makes up the rock surrounding them, just in different forms.