(noun) A hard earthen substance that can form large rocks.
"The stone that the builder refused shall be the head corner stone."
"Dreams are the touchstones of our characters."
"Our wretched species is so made that those who walk on the well-trodden path always throw stones at those who are showing a new road."
"I alone cannot change the world, but I can cast a stone across the waters to create many ripples."
"Never give up. In the end, even the most harmless drop ruins the hardest stone."