A boyhood fascination with rock and rubble led two Long Island brothers, then a recent college graduate and a high school sophomore, to travel south to Brazil. They returned home from their first trip with a knapsack filled with $400 worth of agate ashtrays. Today, Harvey Siegel is the owner of Aurora Corporation, a leading wholesaler of semiprecious, stone, and mineral specimens with an impressive client list that includes the Harverd University Museum, the Smithsonian Institution, H. Stern Jewelers and The Museum of Natural History. The Siegel brothers didnt fly down to Brazil on their buying trip with armloads of research, a long list of connections, or deep pockets. Quite the contrary, Aurora was a seat-of-the-pants operation.