Frank stumbled over something and cursed. Percy brought this sword around for more light. The thing Frank had tripped on was gleaming silver. He crouched down.
“Don’t touch it!” Hazel said.
Frank’s hand stopped a few inches from the chunk of metal. It looked like a giant Hershey’s Kiss, about the size of his fist.
“It’s massive,” he said. “Silver?”
“Platinum.” Hazel sounded scared out of her wits. “It’ll go away in a second. Please don’t touch it. It’s dangerous.”
Frank didn’t understand how a lump of metal could be dangerous, but he took Hazel seriously. As they watched, the chunk of platinum sank into the ground.

The Son of Neptune, Chapter XI