Travertine dripstone in a Virginia cave, USA.

"Cave formations" in caves are technically called speleothem. Most speleothem is composed of travertine, a crystalline-textured chemical sedimentary rock composed of calcite (CaCO3). Travertine forms in most caves and at some springs by precipitation of crystals from water. Pure travertine is white. The colors seen in the travertine shown above are mostly from iron oxides. Travertine speleothem occurs in a wide variety of forms. The most common variety is dripstone, which forms by the action of dripping water - examples include stalactites, stalagmites, columns, and draperies. The second most common variety is flowstone, which forms from flowing films of water. Flowstone has the appearance of a frozen waterfalls.

Shown here is dripstone in Endless Caverns in Virginia. Icicle-like dripstone structures attached to cave ceilings or upper walls are called stalactites. The corresponding structures on the floor are called stalagmites. When fused together, they form columns. Curtain-like dripstone formed as water drips descend along steeply inclined surfaces are called draperies.

The publicly accessible portions of the cave are developed in structurally tilted carbonates of the New Market Limestone (Middle Ordovician). Other portions of Endless Caverns are in overlying units: the Lincolnshire Limestone and the Edinburgh Formation.