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.
Four major types of limestone formations (speleothems): 1  Dripstones: 2  Straws are thin walled hollow formations that resemble drinking straws. As water drips slowly from the roof of the cave, it deposits a microscopic ring of calcite crystal. 3  Stalactites are also formations that grow downwards from the cave roof.