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.
If the droplet falls to the floor and evaporates there, a stalagmite could grow upwards from the cave floor. The limestone that makes up these cave formations is known as travertine and is a chemical sedimentary rock. A rock known as tufa is a limestone formed by evaporation at a hot spring, lake shore, or other area.