We've learned now about sandstone, marble and basalt rock.
There are so many types of rocks!
Another very common rock is limestone, which is a sedimentary rock, mostly made up of types of crystals or small pieces of coral.
(from: wikipedia - limestone)
Most of the caves in the world are made up of limestone, because the stone can be washed away and formed by water flowing against it.
carlsbad caverns national park.
Kid Facts - Blast from the past: Light Bulbs
