How does a stalactite grow from a cave ceiling?

A stalactite grows from a cave ceiling through the deposition of minerals, primarily calcite (calcium carbonate), carried by groundwater.12

The process begins as rainwater infiltrates the soil, absorbing carbon dioxide to form a dilute carbonic acid solution. This acidic water dissolves calcite as it moves through limestone bedrock. When the water emerges from a joint in the cave ceiling, it hangs as a pendant drop.23

As the drop is exposed to the cave atmosphere, it loses carbon dioxide, which reduces the water's ability to hold the dissolved mineral in solution. A small ring of calcite is deposited where the drop contacts the ceiling. As the drop falls and is replaced by another, this process repeats, creating a thin-walled, hollow tube known as a "straw". Over time, mineral deposition from water flowing down the exterior of the pendant thickens the structure into a downward-tapering cone. These secondary mineral formations are collectively known as speleothems.321