The problem is with the question. Rocks exist because God created them. God created them during His creation whose final act of creating was to breathe life into man. At the end of each day of creation God "saw that it was good".
God had a purpose for his creation, rocks included, which God accomplished in the beginning.The question rejects God's stated purpose for His creation and implies that God can and will act without purpose.
At the risk of creating a bad analogy to demonstrate the silliness of the question: Could the contractor build an elevator that goes to the 150th floor of a 100 story building? Perhaps, but why in the world would he want to?
Sorry I distracted you from the first moronic question.