I can be quick and then I'm deadly, I am a rock, shell and bone medley. If I was made into a man, I'd make people dream, I gather in my millions by ocean, sea and stream.

Why this works

This riddle cleverly plays with the multifaceted nature of sand. The phrase "quick and then I'm deadly" refers to quicksand, which is a dangerous mixture of sand and water that can trap someone. The "rock, shell and bone medley" points to how sand is composed of tiny particles of rock, shells, and even organic materials like bones. When sand is made into a man, it suggests a sandman, a character associated with dreams. Finally, the mention of gathering "in my millions by ocean, sea and stream" highlights how sand is found in abundance along coastlines and riverbanks. Each line connects to the properties and contexts of sand, making it the perfect answer to this riddle!