Cave Formations (Speleothems) You Can See While Spelunking

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Beware: You should never explore wild caves alone or without proper gear. Consider getting in touch with a Grotto of the National Speleological Society at or a qualified cave club. These groups are skilled and will train you. Without sufficient knowledge, preparation, and equipment, cave exploring can lead to serious injury or death.

Did you know that caves contain formations that took thousands or tens of thousands of years to form? Caves are just as fascinating and beautiful as they are mysterious. Learning about the types of formations in a cave can reveal much about its history.

You’ve probably seen pictures of caves and wondered how they got those patterns. Well, the answer is simple: water!

The breakdown of rock by running water and other chemicals creates gaps in the bedrock, which then fills with sediment to form a cave.

Over time, as more sediment deposits and is ground up by wind or flowing water erosion, these spaces become more prominent until they are fully-formed caves.

While no one can see all the world’s caves, more than six million in existence, this article covers some of the common cave formations in the world. There are more unique variations of these as well. Cross each off your checklist as you see them in person.

1.   Stalactites

Stalactites grow downward from the ceiling of a cave. They form when water drips from the ceiling of a cave onto the floor. The water then evaporates, leaving behind minerals that makeup stalactites.

These minerals include calcite, which is often white or colorless. The stalactites grow slowly but can become long over thousands of years.

Stalagmites are similar to stalactites except that they grow up from the floor of a cave instead of down from the ceiling.

Stalactites appear in caves with high ceilings and low floors because this is where most of the water can drip down from above.

An image shows stalactites growing above a pool of water inside a cave.
Stalactites hanging from the ceiling above the water in a sea cave.

2.   Stalagmites

Stalagmites form due to the accumulation of mineral deposits that harden over time. The water seeping through the cave drips onto the floor, evaporating and leaving minerals such as calcium carbonate, calcite, or gypsum.

The deposits begin growing upwards until they reach a level where they can no longer increase further due to air exposure.

Sometimes called dripstones, stalagmites spawn when water drops from above and dries up on the floor before starting a stalactite/stalagmite.

Stalagmites grow vertically from the floor. Under similar conditions, depending on the level of moisture, they can grow at different rates.

Calcite and other minerals in the water solution react with the carbon dioxide in the air to form a solid deposit on the floor of a cave. This process is ‘chemical precipitation‘.

3.   Boxwork

Boxwork is a honeycomb-shaped type of speleothem created by water dripping down the walls of a cave. The dissolving limestone creates horizontal layers, which give the boxwork its name.

This intricate pattern appears in caves with large entrances or those with multiple entrances exposed to direct sunlight.

Boxwork can take on different shapes, sizes, and colors. It is usually white or pale yellow in color, and generally comprises calcite and aragonite. Some occurrences may also contain dolomite and gypsum.

One of the cave formations is called boxwork, and this image shows it appears as a honeycomb.
Boxwork at Wind Cave National Park in South Dakota.

4.   Frostwork

Frostwork is a type of speleothem, mineral deposits that form inside caves. It’s formed when water seeps into the cave and freezes.

During the process, water freezes, expand, and forms crystals that stick to the surface of whatever they’re growing on.

Frostwork is found in caves with high humidity (usually from dripping water), low temperatures (between 32°F to 60°F), and a lack of air circulation—all conditions you might find in an underground cave without much airflow.

The crystals can be any size: some are just millimeters long, while others can reach up to several inches long! Some types look like stone or glass, while others look like wood grain or even ferns.

Frostwork formations result when water freezes and forms crystals in caves with high humidity.

5.   Cave Popcorn

Cave popcorn is a type of speleothem. It is created when water drips into a cave and evaporates. The minerals dissolved in the water, including calcite and aragonite, are left behind and form a solid shell around the water droplets.

Cave popcorn and similar formations are also sometimes referred to as ‘coralloids’.

As these deposits gain more layers, they grow taller and larger until they develop into cave columns or stacks (depending on their shape).

Cave formations like this can be found worldwide; however, many are located at sites with great geological significance.

Cave popcorn looks like small bubbles of styrofoam or cotton.

6.   Dogtooth Spar

In a cave with large amounts of water, calcite can build up on the walls and ceiling. This process, known as deposition, occurs when water runs down a cave wall and deposits small calcite particles.

Over time, these tiny deposits add up to form large masses—called dogtooth spars—that hang from the ceiling.

Dogtooth spar is especially common in caves with minimal air circulation or where few animals live in them (like bats).

Dogtooth spar formations in a cave with large amounts of water, appearing like large bubbles of salt.

7.   Helictites

Helictites are needle-like gypsum crystals that grow from a cave’s ceiling. They form when droplets of water containing dissolved gypsum fall from the ceiling, the cool freezing point below, and crystallize on the cave floor.

They are also called “needle ice” because they resemble frozen droplets as seen under a microscope.

Two cavers look up at a helectite bush formation in a cave of Cantabria, Spain.

8.   Calcite Rafts

Calcite rafts are formed when water flows over a flat surface, and the water dissolves the calcite and deposits it in layers, evaporating, leaving behind the calcite. These formations can be large or small, depending on the size of the pool that created them.

The calcite can be transparent or opaque, depending on its dissolved soil. The size of the crystals also varies greatly, some are only a few millimeters long while others are several centimeters in length.

Image shows white and orange calcite rafts, formations found in caves where water flowed over a flat surface.

9.   Flowstone

Flowstone is one of the most distinctive cave formations, as it forms in a very particular way.

When mineral-rich water flows down a cave wall, gently depositing calcium carbonate over time.

Then, as the water evaporates from an underground lake, it leaves behind the minerals in the water. As more and more water evaporates and leaves these minerals behind, they form crystals in layers that look like a stack of plates, and the layers are called “flowstone.”

The flowstone formed by minerals in the water is often beautiful, and it can be clear, white, or colored with other hues like yellow and red.

Flowstone formations found at Carlsbad Caverns National Park.
Flowstone formations in the caves of Carlsbad Caverns National Park

Sometimes flowstones are so thin that they look like glassy sheets of ice lying on top of the cave floor; other times, they can be pretty thick and even have stalactites growing up from them.

Flowstones come in many different types—some resemble rippled sand dunes; others have filigreed patterns similar to frosting on a cake; others look like frozen waterfalls or even coral reefs.

They are usually white or grayish in color, although they can sometimes be red if they contain iron oxides (rust).

When examining flowstone formations, keep in mind that any surface that’s not exposed directly to light will be covered by a thick layer of dust or dirt.


We hope you have enjoyed learning about the different cave formations. We know that it can be hard to remember all of them, and some are more difficult than others. But once you start spotting them in the caves you visit, you will surely remember their names easier. If you’re interested in caving like a professional, it’s essential not only to memorize these names but also how they were created, and what it means about the cave they are in.

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