Our earth has produced rocks that are so flexible that a thin strip will sag under its
own weight. One type of such rock is itacolumite, a type of sandstone whose name is taken
from Itacolumi, a mountain in Brazil where it is found (although it also occurs in North
Carolina (USA), the Ural Mountains, and India).
The sand grains that form the rock are widely separated instead of closely packed like
in regular stones. This property allows it to stretch and bend. However, it is not known
what phenomenon causes the separation. Neither has anyone found a practical use for such
a unique substance.