Aquifer – any geological formation containing or conducting ground water, especially one that supplies the water for wells, springs, etc.

Arthropod – an invertebrate animal with a segmented body, such as an insect or spider

Bedrock – solid rock underlying loose deposits such as soil. In Central Texas, the bedrock is made chiefly of limestone.

Breakdown – an underground rock fall occurring when blocks of rock become detached from the roof of the cave.

Calcium carbonate (Calcite) – CaCO3 – the mineral that is dissolved out of the limestone by carbonic acid and is deposited in our cave to form speleothems.

Carbon dioxide – CO2 – a gas produced by respiration and the decay of plant and animal matter.

Carbonic acid – a mild acid formed when water and carbon dioxide chemically combine. The chemical formula for the creation of carbonic acid is:

H2O + CO2 = H2CO3


Cave – a natural opening in rock extending to points where daylight does not penetrate.

Cavern – a type of cave that grows formations called ‘speleothems’. Some people choose not to differentiate between caves and caverns; others say classification is determined by size. Based on our definitions, just as every square is a rectangle but every rectangle is not a square, you can correctly say every cavern is a cave but every cave is not necessarily a cavern.

Column – a formation touching both the ceiling and the floor of a cavern. Most commonly formed when a stalactite and a stalagmite grow together.

Dark zone – the part of a cave that is always dark, beyond the Twilight Zone.

Debris cone – a mound of dirt accumulated by erosion in what once was an entrance to the cavern. In Inner Space, we call these ‘Bone Sinks’ because they are sinkholes that we found bones in.

Dissolution – The process of chemical weathering of bedrock in which the combination of water and acid slowly removes mineral compounds from solid bedrock and carries them away in liquid solution.

The chemical equation for the dissolution of calcium carbonate in carbonic acid is as follows:

CaCO3 + H2CO3 = Ca+2 + 2HCO3-



Dolomite (or Dolostone) – A calcium carbonate rock (like Limestone) containing magnesium.

Drapery – a speleothem formed by the deposition of calcite along an inclined plane, much like holding a sponge and allowing the water to trickle down your arm. Cave bacon is a type of drapery.

Flint (Cryptocrystalline quartz) – a sedimentary rock consisting mainly of silicon dioxide, which may come from animals such as sponges. Flint is the hardest rock in Inner Space Cavern.

Flowstone – a speleothem formed from the precipitation of calcite over cavern floors and walls.

Fluvial – pertaining to flowing water.

Groundwater – water below the level at which all voids in the rock are completely filled with water.

Karst – a landscape formed from the dissolution of soluble rocks including limestone and dolomite, generally characterized by sinkholes, caves, and underground drainage systems.

Larva – the active, immature form of an insect Limestone – a sedimentary rock consisting mainly of Calcium Carbonate from the shells of aquatic animals. Many caves are found in Limestone because of its high solubility.

Permeability – the property of rock or soil that permits water to pass by flowing through interconnected voids (the porousness of rock.) Aquifers are made of permeable bedrock.

Phreatic – noting or pertaining to groundwater.

Precipitate – to separate a solid from a solution (in relevance to the cave, the separation of calcite from the carbonic acid solution).

Saturated – holding as much water or solute as can be absorbed.

Sediment – material deposited by or precipitated from water, often made from small rocks and dead organisms.

Sedimentary rock – rock formed at the bottom of an ocean or sea from an accumulation of sediment.

Sinkhole – a closed, often bowl-shaped surface depression draining underground in karst landscape. Sinkholes form when the ceiling of the cave is dissolved or eroded away to the point where it can no longer support its own weight and collapses.

Soda straw – a completely hollow formation growing from the ceiling of a cavern. A drop of water clings to the ceiling, and the calcite precipitates around the drop of water. The rings form one under the other, like stacking Cheerios upside-down.

Soluble – able to be dissolved

Solute – a substance that is dissolved into another

Solution Cave – a cave formed from slowly moving ground water dissolving away the carbonate bedrock.

Solvent – a substance that dissolves another

Speleology – the exploration and study of caves

Speleothem (Formation) – a deposit formed in caverns by the chemical precipitation of a mineral, usually calcite, from water.

Stalactite – any formation growing downward from the ceiling of a cavern. When the tip of a soda straw becomes blocked with calcite, the formation begins to grow thicker due to the precipitation of calcite on the outside of the formation. All stalactites start out as soda straws, and are therefore hollow.

Stalagmite – any formation growing upwards from the floor of a cavern. Often found beneath stalactites, stalagmites form when a drop of water saturated with calcium carbonate falls to the floor, where the calcite then falls out of solution. Because water splashes when it hits the ground, stalagmites tend to be wider than the corresponding stalactites above them.

(The previous two words sound very similar. One fun way to distinguish between them is the saying “Stalactites hang ‘tight’ to the ceiling, stalagmites ‘might’ reach the ceiling someday.” Or it can be pointed out that ‘stalactite’ has a ‘c’ for ‘ceiling,’ and ‘stalagmite’ has a ‘g’ for ‘ground.’)

Transition zone – initial region of the Dark zone in which there is no light, but some external factors from the entrance environment may still be apparent, such as seasonally fluctuating air temperatures.

Translucent – permitting light but not image to pass through.

Troglobite – an animal that lives in a cave and is unable to exist outside of it. These animals have adapted to live in total darkness, and exhibit physical traits such as blindness or complete lack of eyes, long feelers, and lack of pigmentation. The Eurycea rathbuni (Texas Blind Salamander) is a troglobite.

Troglophile – an animal which frequently completes its life cycle inside caves, but is not confined to them. Cave crickets are troglophiles.

Trogloxene – an animal which spends only part of its life cycle in caves, and which often exits the cave in search of food. Bats are trogloxenes.

Twilight zone – the part of a cave in which some daylight but no direct sunlight penetrates.

Water table – the level below which the ground is saturated with water