After seeing Rebecca and other skepchicks at the recent Amaz!ng Meeting 7, I realized that it’s time to start writing for Skepchick again. My geology word of the week slipped to a geology word of the month, so to make up for that I’m going to post a triple feature of geology words this week. I’ll post one word today, one on Monday, and one on Wednesday. After this kickstart, I’ll go back to my weekly word and try to write up some other skeptical tidbits now and again.
That said, the first geology word of the week is: Speleothem. I was working on some speleothem samples this morning in lab, so I thought this would be a fitting word for today.
If you’ve ever been to a cave, you’ve probably seen speleothems. Speleothem is an encompassing term which is used to describe all types of chemical precipitate minerals that form in caves. Speleothems generally precipitate from groundwater which has percolated through the bedrock surrounding the cave and leached various elements and compounds. When the enriched water reaches the cave, changing conditions (a large open space has very different pressure and temperature than pore spaces in bedrock) allow gases, such as carbon dioxide, to escape from the water. Evaporation can also occur. The changing composition of the water encourages the (usually very, very slow) precipitation of speleothem minerals from cave waters.
Chemically, the speleothems which form in a particular cave are similar in composition. Most caves are formed in limestone, and so the speleothems will generally be formed of calcite, the dominant mineral in limestone. However, depending on how and where the speleothem is precipitated, it can take on a variety of shapes. Scientists and other cave explorers have given different names to these various morphologies. Examples of speleothems are stalactites, stalagmites, flowstones, cave coral, cave drapery, cave curtains, and cave crystals. There are dozens of names for various cave formations, so speleothem is a nice catch-all phrase for geologists to use.
Most speleothems form over thousands upon thousands of years. Thus, you shouldn’t touch or remove speleothems unless you’re doing so for legitimate science. Even when collecting speleothems for science, one should be conservative. Take small samples and obtain the necessary permissions. Fortunately, for my own research in Oman I am often able to collect speleothems which have fallen on the ground and are no longer growing.
Here’s a picture of me with a stalagmite in Oman. I didn’t sample this one, but I did sample some of its neighbors. This particular stalagmite isn’t forming in a true cave but rather in an open hallow underneath a layer of rock. Water percolated through the layer of rock and formed speleothems in the hallow underneath. I’ll try to write more about my research in Oman in coming weeks.
Now, for those of you who still confuse stalactite and stalagmite, here’s a reminder of something you probably learned in grammar school but may have forgotten by now.
StalaCtites hang tite to the Ceiling while stalaGmites grow up from the Ground.