Which compound is the primary component of natural pearls and seashells?

Calcium carbonate

Which 2013 film features Sandra Bullock and George Clooney stranded in space? What do grapes turn into when dried? What city became the first capital of the United States after independence? In the first episode, whom does Rachel come to look for? What FPS video game featured jetpack combat and wall-running, developed by Respawn Entertainment?