🕳 Stalactites
A stalactite grows downward from a ceiling as mineral-rich water drips, leaving a thin ring of mineral each time. Calcite builds them in limestone caves. Inside volcanic gas pockets, chalcedony, amethyst, apophyllite, rhodochrosite and malachite build them too. Sliced across, they show bullseye rings or a flower-like star.
1 · A drip
Water carrying dissolved minerals seeps through a cavity roof and hangs as a drop.
2 · A ring
The drop loses CO₂ or evaporates slightly and leaves a ring of mineral. Ring by ring, a hollow 'soda straw' grows.
3 · Thickening
Water also runs down the outside and adds layers like tree rings. Later, crystals such as amethyst or apophyllite may coat the column.
Collecting note
Cave formations are protected in many places, including US national parks and federal caves. Buy specimens from mines and reputable dealers.
