Asteroid of the Damned by Frederik Pohl

"Sorry, son," MacCauley said with the barrel-scrapings of his patience. "I said no and I meant it. I haven't got anything to give you. Now please stop waggling at me and go."

The excited glitter of the Palladian's luminiferous eyes died dispiritedly. MacCauley turned his back on the slight-bodied asterite and rapped his thumbnail against his drained glass. The bartender, a heavy and humorous man, expertly refilled Mac's glass with oily, musky, milk-white synthetic liquor and said: "This Kiddie bothering you? Scat, you, or I'll see that you never get into this place again."

Mac shrugged as he watched the stripling strain to catch the bartender's meaning by reading his lips, then mournfully disappear. "No more than they all do," he answered. "What's the matter with them, anyhow? They're positively nutty on the subject of money."

The bartender shook his head and snatched a quick drag on a smoldering cigar-stub. Replacing it on a ledge, he said: "Not money so much. You couldn't bribe a Kiddie with a certified check for a couple of billion dollars. They're not bright, exactly; they don't regard paper as worth anything. It's metal they want. If it happens to be precious, that's all right, but any kind of metal will do. What they're really crazy about, of course, is silver and copper. They'll do just about anything for it, including murder and treason."

Mac, listening too intently, gulped a bit more of his drink than even his spaceman's gullet could take. When the red-hot lava stopped strangling him and he could see once more through the streaming fountains that had been his eyes, he managed to choke out: "What do they want it for? Do they eat it?"