What word means a mineral deposit formed inside a cave?

The word for a mineral deposit formed inside a natural cave is speleothem.

Speleothems develop when dissolved minerals are deposited from groundwater, seepage, drips, films, or pools inside a cave. The term includes familiar formations such as stalactites, stalagmites, flowstone, soda straws, curtains, and columns. Most are found in limestone or other carbonate caves and are composed mainly of calcite or aragonite, both forms of calcium carbonate.

The chemistry begins above ground: rainwater picks up carbon dioxide from the atmosphere and soil, then becomes weakly acidic and dissolves carbonate rock. Once the water enters a cave, changing carbon-dioxide pressure and evaporation can cause minerals to precipitate. Repeated deposition gradually creates the visible formation.

Speleothems are more than scenery. Their layered growth can preserve clues about past rainfall, vegetation, and climate. The term generally excludes similar deposits produced by concrete, mortar, or other human-made materials; those are commonly called calthemites.