Danielle has taught middle school science and has a doctorate degree in Environmental Health
What Is a Stalactite?
Imagine you enter a cavern and look up to see a beautiful collection of minerals hanging like frozen teardrops from the ceiling. The beauty of nature amazes you as you stand in awe looking at all of the gorgeous stalactites. Time out, wait just one minute, a stal-act-what? Oh yes, you read that word correctly. Stalactites are structures formed from mineral deposits that hang from caves. A great way to remember the term stalactite is to think of the phrase, 'hang tite'--afterall, these formations hold tightly to the ceiling and hang down.
There is a very important point regarding stalactites: Be careful not to confuse them with their sisters, stalagmites. As opposed to hanging from the ceiling, stalagmite structures are formed from the cave floor that point upward. A great memory tool to ensure you never confuse the terms is to remember the 'c' in stalactite stands for ceiling, while the 'g' in stalagmite stands for ground. In the image shown below, test your ability to identify a stalactite from a stalagmite.
Going back to stalactites, if you happen to travel to different caves, you may encounter different types of stalactites. Stalactites come in a wide variety of types, such as deflected stalactites (that form in a curve) and elephant's foot stalactites (that takes on a flatter form).
In All Its Glory: Formation of Stalactites
Nature's way of forming stalactites is very fascinating. The shape of stalactites can be thought of as an icicle-shape structure, as shown in the figure below. They tend to have pointed tips like the end of a pen or sharpened pencil.
As we saw in the definition of stalactites, these structures are composed of minerals. Examples of minerals found in the stone of caves containing stalactites range from opal and limonite to carbonate and chalcedony. The most common stone found in caves with stalactite is limestone, which contains the mineral calcite. In fact, this mineral is found not only in limestone, but also in most sedimentary rocks.
Can you guess what calcite is made of? Right on! Calcite is made of calcium and carbonate ions. A fancier, chemically correct way of naming calcite is 'calcium carbonate' The molecular formula for calcium carbonate is CaCO3. Let's say you enter a cave to escape a rain cloud. Inside the cave, you hear and see rainwater flowing through the cave. This rainwater plays a very important role in forming stalactite. When the water trickles through the rocks, inside the cave, minerals from the limestone as well as carbon dioxide in the air is picked up by the water. As shown in the equation below, when carbon dioxide mixes with rainwater, carbonic acid is produced. Interaction between calcite and carbonic acid results in the formation of calcium bicarbonate.
The molecular formula for calcium carbonate is Ca(HCO3)2. Think of this compound as the form of calcite after swirling it in rainwater and allowing it to dissolve. Traveling through the cracks in the ceiling of the cave, calcium bicarbonate can transform back into calcium carbonate. Recall that calcium carbonate is the chemical name for calcite.
While traveling, calcite will settle into the cracks and crevices of the cave. As more water continues to drip, it brings along more calcium bicarbonate that can be converted to calcite. Over time you get layers and layers of calcite forming in these cracks, eventually leading to the development of a stalactite. As you might suspect, the time it takes to make a stalactite can be quite long. In fact, it is estimated that one inch of stalactite or less grows every 100 years.
Whether you are traveling through a Bermuda cave or exploring a cavern in your local town, the next time you look up and see a stalactite reflect on the wonder of this structure and nature's process of forming it.
Stalactites are fascinating structures made from mineral deposits that hang from the ceilings of caves. Stalactites come in a variety of different types, such as the deflected or elephant's foot stalactites. As rainwater enters a cave, calcium bicarbonate converts to calcium carbonate. Calcium carbonate is the chemical name for calcite. The accumulation of calcite into the cracks of the cave's ceiling forms a stalactite. It takes roughly 100 years for a stalactite to grow up to one inch.
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