Grape Agate is a unique and distinctive mineral known from only a few locations on earth. Not technically an agate, it is instead formally known as botryoidal purple chalcedony. Named for the small spherical crystal nodules, these individual grapes can range in color from turquoise to deep purple, depending on the presence of minerals like manganese or iron during the formation of the crystals. Grape agate is a relatively new mineral and sought after by collectors due to its scarcity and vivid color.