What grows faster from stalactites and stalagmites?

I'd guess stalagmites. Stalagmites are formed when water and acids are dripping from a stalactite...for a stalactite to form there must be years of oxidization, but I guess a stalagmite could be made at 4-5 years...

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They probably grow at similar rates, at least by volume if not necessarily by length, and the rate is probably fairly specific to the individual site.

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Add 00 to those figures. None have been found to grow in 4-5 years, though scientists studying deposits in one Italian caves were startled to find a glass bottle only a few decades old inside one stalagmite! That is exceptionally fast. Normally, these formations, which grow by precipitation of calcium carbonate, not by oxidation or dripping acids, take hundreds or thousands of years to grow.