Asinkholecould form if the roof of an underground cave collapses. Some sinkholes are
large enough to swallow up a home or several homes in a neighborhood (Figure10.10). As
groundwater dissolves away solid rock, it carries those minerals in solution as it travels. As
groundwater drips through openings, several interesting types of formations occur.Stalac-
titesare icicle like deposits of calcium carbonate which form as layer on layer of calcite drips
from the ceiling, coating the ‘icicle’ (Figure10.11). As mineral rich material drips to the
floor of a cave,stalagmitesform rounded deposits of calcium carbonate on the floor of the
cave. The word stalactite has a ‘C,’ so you can remember it forms from the ceiling, while
the ‘G’ in stalagmite reminds you it forms on the ground. If a stalactite and stalagmite join
together, they form a column. One of the wonders of visiting a cave is to witness the beauty
of these amazing and strangely captivating structures. Caves also produce a beautiful type
of rock, formed from calcium carbonate calledtravertine.This happens when groundwater
saturated with calcium carbonate suddenly precipitates out as the mineral calcite or arag-
onite. Mineral springs that produce travertine can be hot springs or the water may just be
warm or could even be cold (Figure10.12).
Figure 10.10: This sinkhole formed in Florida. ( 50 )When lots of calcium carbonate is carried by groundwater, we call the water ‘hard.’ If the
water in your area is hard, it might be difficult to get soap to lather or make soapsuds. Hard
water might also have a taste to it, perhaps one that some people don’t like as much as pure
water. If your water is ‘hard,’ you may treat your water with a filter before you drink it.
Zeolites are minerals that help to absorb ions from the water as it passes through the filter.
When the water passes through the filter, it comes out tasting good!