For those who enjoy exploring caves, there are a variety of different types of formations worth looking at. For limestone caves, these will primarily involve stalactites and stalagmites. These formations have taken hundreds of years to form, with some of the most impressive ones being nearly 20 feet in length. Be careful not to touch these formations, as oils in the skin can essentially kill the growth of the formation.
Stalactites can be founding hanging from the ceiling of limestone caves. They are formed by calcium deposits found in droplets of mineralized water that travels through the rocky ceiling of the cave. When the water evaporates, it leaves behind a calcite deposit that eventually forms a stalactite. Stalactites resemble icicles. The average growth of a stalactite per year is roughly 0.13mm.
Stalagmites grow upward from the floor of a limestone cave. Stalagmites are formed much in the same way as stalactites, from the evaporation of mineralized water that forms a calcite mound that grows upward. Water dripping from a stalactite will drip down to the cave floor and evaporate, leaving behind the calcite deposits that will eventually form stalagmites. Often, stalactites and stalagmites are found in pairs. Columns are formed when a stalactite and a stalagmite fuse together to form one floor-to-ceiling pillar.
Soda straws are formed when mineralized water flows through cracks in the rocks of a cave. The water evaporates, leaving behind a ring-shape mineral deposit. As more water flows and evaporates, the calcite deposit gets bigger and forms a hollow formation like a soda straw. Soda straw formations can grow long but are also extremely fragile. Soda straws grow quickly and have been known to grow several centimeters per year.
Helictites are a type of cave formation that changes its axis during its growth, taking on a contorted appearance. Helictites are formed through water deposits in the pores of the rock that evaporate and leave behind a calcite deposit. It is thought that helictites have a central capillary channel that allows the water to flow through and leave its deposits, like a straw. The twisted shapes that a helictite can take are thought to be because of a number of factors, including impurities in the calcite, the central channel at one time having been blocked and then later becoming unblocked, and also air currents.