Soda straw

Soda straws grow in places where water leaches slowly through cracks in rock, such as on the roofs of caves.

[1] A soda straw can turn into a stalactite if the hole at the bottom is blocked, or if the water begins flowing on the outside surface of the hollow tube.

Kartchner Caverns in southern Arizona has well-preserved soda straws because of its recent discovery in 1974 and highly regulated traffic.

[2] Straws can also form beneath man-made structures and grow significantly faster than in the natural cave environment.

[5][4] Their chemistry differs from those found in caves because they are derived from concrete, lime, mortar or other calcareous material.