Giant Geodes
Part of Allison and Roberto Mignone Halls of Gems and Minerals.
Daniel Kim/© AMNH
One of the largest specimens in these halls, this dazzling geode is 9-feet tall (2.7 m) and weighs around 11,000 pounds (4,990 kg)—as much as four compact cars! Its “sibling” specimen is taller, at 13 feet (4 m), but lighter at 9,040 pounds (4,100 kg).
Geodes are composed of quartz, the second-most common mineral on Earth, which makes up most of the sand on our planet’s beaches. In a process that began 135 million years ago, colorless quartz crystals eventually turned into purple amethyst through natural radiation, heat, and trace contaminants.
The rim of this specimen is white, gray, and brown chalcedony—a variety of quartz with ultra-small crystals.
