dish soap, warm water & a scrub brush will do them no harm, marbles don't scratch easily unless you use some type of abrasive or chemical cleaner, diggin is fun anyway
Backlight them and look for a fiery glow like Arts, no glow no Moonie. The glass must be opalescent for it to qualify as a Moonie. Even under a low light the mibs should exhibit some opalescence if Moonies. Indirect sunlight (daylight) works very well as in Arts pic.