Created by the interaction of water, calcium bicarbonate and limestone, the distinctive cave formations of stalagmites and stalactites are often mistaken for each other. Stalagmites grow upwards from the floor of a cave, formed by drips of water saturated with calcium bicarbonate. Stalactites, made of a similar deposit of crystalline calcium bicarbonate, grow downwards, like icicles. Both are formed by water and calcium bicarbonate filtering through limestone and partially dissolving it. In limestone caves, stalagmites and stalactites are usually white (from the limestone) or brown; in caves where copper deposits are present colours might be more psychedelic, with iridescent greens and blues. They often become united, over time, in a single column.

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