Make a stalactite and a stalagmite!

Take a look at a picture of the inside of a cave (click here to see some wonderful pictures online).  Do you see all those pointy formations on the roofs and floors that look a bit like icicles in winter?  Believe it or not, those are not ice!  The ones hanging down from the roofs are called stalactites, and the ones sticking up from the floors are called stalagmites.  What are stalactites and stalagmites, and how do they form?

Most commonly, stalactites (also called 'dripstones') and stalagmites are found inside limestone caves (a cave is just a large, open space that is underground).  They form when water seeps through the rocks above, picking up minerals along the way, and finally seeping through the cracks in the cave's ceiling where it drips down onto the floor. 

---

As the mineral-laden water drips from the ceiling to the floor, it leaves some of those minerals behind. 

---

Slowly, drop by drop, the dripping water deposits enough minerals for this icicle-like shape to form, both on the ceiling of the cave and on the floor, where the drops land. 

This is a very, very slow process--a typical stalactite will grow only 0.0051 inches per year!  That's only about the width of a human hair!  You can just imagine how old those big stalactites and stalagmites in the pictures you saw must be!

---

TRY MAKING YOUR OWN STALACTITE AND STALAGMITE!

Here's what you need:

1 cup Epsom salts

2 small cups (about 6 oz each)

1 piece of cotton string, 12 inches long

2 metal washers or small bolts

1 piece of cardboard, 6 inches by 10 inches

some water from your kitchen sink

a ruler


Here's what to do:

1. Pour half of the Epsom salts into each cup.
2. Add just enough water to cover the salts in each cup, and stir each for about 30 seconds (don't
   worry, not all the salts will dissolve).
3. Soak the string in water, and squeeze out the excess.
4. Tie one washer to each end of the string, and put each end into one of the cups.
5. Place the cups on the cardboard, far enough apart that the middle of the string hangs about 1 inch
   from the cardboard.
6. Place the cardboard and cups somewhere where they will be left alone, such as on a shelf in your room, or on the counter in your kitchen (ask your parents' permission first!). 
7. Watch the middle of the string, just where it gets closest to the cardboard.  You should see the water start to slowly drip from the string to the cardboard.
8. Observe the cups and string every day at the same time for at least 7 days.  Each time write down what you see.  Very carefully use your ruler to measure how long the stalactite is each day.  BE CAREFUL NOT TO TOUCH IT, OR IT MAY BREAK!
9. Allow the cups and string to sit longer, another 7 days if possible, and continue writing down what you see each day.  Be sure the cups still have some water in them, and add some water if needed.

This is what your experiment should look like: two cups with Epsom salts and water, a piece of string with a washer at each end hanging between the glasses, all on top of a piece of cardboard.

---

How long was your stalactite after 7 days?  After 14 days?  How much did it grow each day?  You can calculate the average growth per day by taking the length after 14 days, subtracting the length at 7 days, and dividing by 7, like this:

(Length after 14 days - Length after 7 days)       =        Average growth per day
7                                                         

Did your stalactite grow fast or slow, compared to average?


MAKE UP YOUR OWN EXPERIMENT!

How else could you get a stalactite to form?  Remember, a stalactite is just a formation made by the deposition of some solid by dripping water. 

Another type of stalactite is an icicle, which is just a stalactite made from frozen water!  If it's cold outside, try to make an icicle by using a paper cup of water with a tiny hole in the bottom.  Make a few holes in the sides of the cup, just under the rim, and tie the ends of a single piece of string to each hole.  You can make the tiny hole in the bottom of the cup using a needle or a pin (get your parents' help!).  Hang the cup over a branch outside, and fill it with warm water.  Wait and see what happens!