Who's This? Turn to page 11 in your guide book (Who's Who vol.XXII). That guy.
How you could have heard of him: You couldn't. Hey, you think Mayor Thomas Bolt would make a good character for Arrow? His story seems perfect for the show.
Example story: Detective Comics #560-565 (1986) by Joey Cavalieri (writer); Jerome K. Moore and Stan Woch (pencilers); and Dell Barras, Steve Montano and Rodin Rodriguez (inkers)
Seems like a pretty interesting idea for the TV series or even the rebooted GA series, no? They kept it so short, there seems to be some untapped potential left.
Who else? Other mineral heroes in Who's Who volume XX include Star Sapphire (well-known), Steel (soon dead and eventually replaced by someone cooler, but I think we know this guy well enough), Sterling Silversmith (thought about it, but not this round) and Stone Boy (the Legion of Substitute-Heroes is NOT obscure, I swear). No, next I think we're going to go the other direction... in time.