Formations of Jewel Cave

The "Jewels" of Jewel Cave

Jewel Cave get its name from the abundant calcite crystals that decorate its walls. This calcite crystal typically appears in the form of nailhead spar and dogtooth spar (shown below). These crystals formed as acidic water carved away our limestone rock, forming the passageways we explore today. As the water became less acidic, the calcium within the water precipated a layer of calcite spar that covered all surfaces of the cave.

Opaque crystals with black spots.
The blunt surface of nailhead spar seen up-close.

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Nailhead Spar

How it forms: Nailhead spar crystal formed in an underwater environment. The built up calcium from the eroded limestone precipitated or stuck to the walls of the cave. Water filed down the tops of the crystal to be flat, similar to the flathead of a nail.

Fun Fact: At one point in Jewel Cave’s geoglogical history, the walls and ceiling were 100% covered in calcite crystal.
Sharp pointed crystals in a hole in limestone.
A close-up view of a pocket of dogtooth spar.

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Dogtooth Spar

How it forms: Dogtooth spar adorns cavities, veins, and other areas of Jewel Cave. This crystal has a pointed tip, differing from nailhead spar. A combined version of dogtooth spar and nailhead spar is found within the cave, where some crystals are semi-pointed.

Fun Fact: Dogtooth Spar is named after its resemblance to canine teeth.
Many crisscrossing brown stone fins creating a grid shape on a cave ceiling resembling a spider web.
An example of boxwork at Wind Cave National Park.

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How it forms: Boxwork is as a “honeycomb-like” structure that forms in fractures of sedimentary rock. Within these fractures, gypsum mineral dried and rehydrated. Calcite then seeped into these fractures and solidified to take on the shape of the original gypsum crystals.

Fun fact: Boxwork gets its name from its resemblance to post office boxes. Most of the world's known boxwork can be seen at Wind Cave National Park.
A soda straw hanging from the ceiling with a drop of water at its tip.
A soda straw hanging from the ceiling with a drop of water at its tip.

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Soda Straws

How it forms: Soda straws resemble hollow tubes, similar to the straws we drink from. They form as water leaches slowly through cracks in the ceiling of the cave. As a water drop hovers on the tip of this formation, it deposits a ring of calcite. The drop of water then falls, and a new drop takes its place. These formations are some of the most fragile speleothems found in caves.

Fun Fact: If the tip of a soda straw gets blocked by minerals or if water begins flowing on its outside surface, it becomes a stalactite.

Stalactites hanging from the ceiling.
Stalactites hang down from the cave ceiling.

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How it forms: Stalactites from where water comes into the cave through fractures in the rock above. When the water reaches a room, it degasses, and leaves behind a small deposit of calcite, which, over time builds up to form a longer stalactite.

Fun fact: Stalactites are found on the ceiling of caves. To remember this, just keep in mind stalactite has a "c" in it for ceiling!

A calcite deposit develops up from the floor of the cave.
A stalagmite on the floor develops upwards towards a stalactite.

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How it forms:Stalagmites are formed when the water drips from the cave ceiling and leaves another deposit of calcite on the ground below. With each drop of water falling onto it, a stalagmite will continue to develop taller and wider.

Fun Fact: Stalagmites are on the floor, or ground, of a cave. This can be remembered as stalagmite is spelled with a "g" for ground!

A cave explorer stands beside a pilar of calcite that is twice as tall as them.
A caver looks up at a large, broken column.

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How it forms: Columns form when a stalactite and a stalagmite meet together, forming a pillar-like speleothem. Once a column is formed, water will travel on the outside of the formation, causing the column to become wider over time.

Fun fact: Along the Scenic Tour of Jewel Cave, you will have the chance to see a soda straw column that is over four feet long.
Rounded calcite formations resembling popcorn sit along a cave wall.
A close-up view of cave popcorn on a cave wall.

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Cave Popcorn

How it forms: This calcite formation froms from water seeping through cave walls or splashing onto them. As the water comes in, deposits of caclcite are left behind when carbon dioxide loss causes the water's minerals to precipitate, or solidify, on the cave surface.

Fun fact: Cave popcorn can be seen along the Scenic Tour route and can be discolored due to other impurities within the water.
A calcite strand discolored reds, oranges, and yellows, similar to bacon, adorns the cave wall.
The iconic strand of cave bacon, a type of drapery, seen along the Scenic Tour route at Jewel Cave.

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How it forms: This is a sheet-like deposit of calcite that forms where water flows down the walls, floor, or other formations within the cave. Flowstone can appear in a variety of forms within caves, such as draperies or ribbons (cave bacon). Draperies form as calcium rich water flows along overhung rock surfaces or walls in a cave. Ribbons, or cave bacon, tend to be isolated drapes, where one thin layer of calcite forms as water moves down overhung walls in the cave.

Fun fact: Jewel Cave's Scenic Tour route is well-known for a twenty foot long ribbon or strand of cave bacon.
Small, delicate, silver-colored, inflated balloons attached to the cave wall.
Hydromagnesite balloons attached to the cave wall.

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Hydromagesite Balloons

How it forms: Hydromagnesite speleothems are a by-product of frostwork or cave popcorn. When calcite and aragonite crystallize out of water coming into the cave, magnesium becomes more concentrated than calcium in the remaining water. In areas of very high evaporation, the magnesium will precipitate out as hydromagnesite. Hydromagnesite appears on the cave walls as small white clumps. Rare hydromagnesite balloons exist in a few areas of the cave, where the pasty material has been inflated. These delicate balloons are only a thousandth of an inch thick.

Fun fact: This formation was first found at Jewel Cave, and we are only place in the world you can see this formation on a public tour, the Wild Caving tour.

Gypsum Formations

Calcite speleothems are not the only type of formations adorning Jewel Cave. In drier parts of the cave, gypsum features can be found in a variety of forms. These gypsum formations appear as gypsum needles, gypsum spiders, gypsum beards, and gypsum flowers. It is not entirely known how these various features form.
Thin strands of gypsum shoot up from the cave's floor. Thin strands of gypsum shoot up from the cave's floor.

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Gyspum needles on the cave floor.
Credit: NPS Photo

Right image
Gypsum spiders cling to the cave ceiling.
Credit: NPS Photo

Hair-like strands of gypsum hand down to cotton-like pile of gysum. Hair-like strands of gypsum hand down to cotton-like pile of gysum.

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A gypsum beard hangs down from the cave ceiling.
Credit: NPS Photo

Right image
A gypsum flower hangs from the cave ceiling.
Credit: NPS Photo

Last updated: September 15, 2023

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