You are a US citizen and: 1  You are a first time applicant age 18 or older. 2  OR your most recent U.S. Passport was issued when you were under age 16. 3  OR your previous U.S. passport was issued more than 15 years ago.
Cave formations are called speleothem, from the Greek word spelaion, cave and thema meaning deposit. Almost all of them are made of calcite, the crystal of calcium carbonate. Different minerals and different movements in the water account for an incredible variety of cave formations.
Calcite is the primary mineral component in cave formations. Stalactites and stalagmites, cave veils, cave pearls, soda straws and the many other different cave formations that millions of visitors to underground caverns enjoy are made of calcite.