Explore the stories behind the Smithsonian’s National Gem Collection during an online program — courtesy of Mentor Public Library — at 2 p.m. Dec. 4. The program will be led by Jeffrey Post, emeritus curator and author of “The Smithsonian National Gem Collection Unearthed: Surprising Stories Behind the Jewels.” He’ll share the scandals, mysteries and human stories behind the world’s greatest gems, including the Hope Diamond, Star of Asia Sapphire, Carmen Lucia Ruby, Blue Heart Diamond and more, according to a news release. Sign up to join the conversation at libraryc.org/mentorpl. A recording of the program will be available to watch afterward.