The $20/year subscription helps cover the costs of producing new videos, writing curriculum units, site development, and hosting. Without that support, this site would not be possible.

If you are already a subscriber, and having problems logging in, please check the Support Page.

If you are not yet a subscriber, please check out the Free Stuff page, and Subscribe Now.

A Homemade Barometer

Using common, household materials, we can construct a simple barometer to measure changes in air pressure.

The $20/year subscription helps cover the costs of producing new videos, writing curriculum units, site development, and hosting. Without that support, this site would not be possible.

If you are already a subscriber, and having problems logging in, please check the Support Page.

If you are not yet a subscriber, please check out the Free Stuff page, and Subscribe Now.

The $20/year subscription helps cover the costs of producing new videos, writing curriculum units, site development, and hosting. Without that support, this site would not be possible.

If you are already a subscriber, and having problems logging in, please check the Support Page.

If you are not yet a subscriber, please check out the Free Stuff page, and Subscribe Now.

Once you understand the general idea of intrusive and extrusive rocks, it helps to see the process in action. If you don't happen to have a volcano nearby, there is a fun, easy, and tasty way that you can explore the difference between how rocks form from magma and lava.

Sorry, but this content is reserved for subscribers only.

Your $20/year subscription helps cover the costs of producing new videos, writing curriculum units, site development, and hosting. Without that support, this site would not be possible.

If you are already a subscriber, and having problems logging in, please check the Support Page.

If you are not yet a subscriber, please check out the Free Stuff page, and Subscribe Now.

---

Home - Rocks - Igneous Rocks

I first became interested in rock stacking during our trip to Technorama, the Swiss Science Center. Thorsten Künnemann, their Executive Director took us on a marvelous tour of Zurich. As we walked along the shore of Lake Zurich, we came to an area that was filled with amazing stacks of balanced rocks. When you first see them, you think that they must be held together with glue or mud. Only when you get very close can you see that it is all a matter of balance. Since then, we have seen similar stacks in other places and made some of our own.

If you would like to try rock stacking, you will need:

• a flat, stable surface
• a variety of rocks or other things to stack
• steady hands
• lots of patience

While at first rock stacking may seem like a frivolous activity, there is actually quite a bit of science and engineering involved. As we saw in the Science of Balance video, we can balance an object by keeping its center of gravity (its balancing point) directly above its base (the part of the object that is supporting it.)

To start, you need a wide variety of rocks, or other objects to stack. If you don't have lots of large rocks, you might try stacking toys, stuffed animals, or other irregularly shaped objects that are not breakable.

Select a large, steady rock as your foundation. You want the rock on the bottom to be very stable, because if it wobbles, your entire stack will wobble, which usually means that it all falls down. By using a wide, flat rock, it has a large base, which gives you plenty of working room to keep the center of gravity inside that base. While you are learning the art of rock stacking, you will have better success if you also choose a foundation rock that has a fairly flat top, to make it easier to balance the next rock.

It is easiest if you start simply, using fairly flat rocks to make stacking easier. Keep in mind that as you add each rock, you are adding pressure to the rocks under it, which may shift their center of gravity. Work slowly. Instead of putting a stone in place and releasing it, gradually let its weight rest on the stack, checking to see whether the stack remains stable.

Once you have the knack of stacking flat rocks, then you can start to get more creative and adventurous. Use rocks with unusual shapes, and try balancing them on smaller bases. Remember that a smaller base means you have to be more careful with the stack's center of gravity. Also remember that each rock can change the center of gravity of the entire stack, throwing the stones below it out of balance. If one orientation is unstable, try turning the rock to a different side. If that does not work, then try a different stone. The more you practice; the more you will learn about the art and science of stacking rocks.

Several people have written me lately, asking how to make simulated geodes in egg shells. Geodes are pockets of crystals that form in sedimentary and igneous rocks. They start as hollow spaces in rock that is porous enough for water to seep through. The water carries dissolved minerals, which are deposited in the open space, forming a lining of crystals. Most geodes contain quartz crystals, but they can also contain calcite, celestite, and other minerals.

Many rock shops and museum gift shops sell geodes that have been cut, and sometimes dyed to make them more colorful. Sometimes you can buy unbroken geodes, which lets you break them open yourself. That is particularly fun, as you never know how it will look until you open it.

If you don't have a place to collect geodes, you can make quick, easy, simulated geodes by using egg shells for the hollow spaces. I have seen several different recipes, many of which take days, but you can make an egg shell geode in a few hours by using epsom salts for the crystals. We will be using basically the same formula that we used for Growing Crystals from Solution, so you will need:

• several egg shells, washed and cleaned
• an egg carton to hold the shells
• epsom salts, available at pharmacies and grocery stores
• hot water
• a measuring cup
• a refrigerator
• food coloring

Start by making an omelet or something else yummy that requires eggs. For the best results, crack the eggs close to the small end of the egg. This leaves you a fairly large egg shell to use. The larger the egg shell, the more crystals you will have. Wash the shell, and remove the skin-like membrane that lines the shell. For short term projects, you can leave this membrane in place, but you should remove it if you plan to keep your geode for a long time, as the membrane tends to mold after a while.

Depending on how many eggs you are going to use, you may not need as much of the solution as we used before. I tried using 1/4 cup of epson salts and 1/4 cup of hot water, and it worked fairly well for 6 egg shells. You want the water to be hot, but not boiling. Stir in the epsom salts. If it all dissolves, add another spoon full. Place the egg shells in the egg carton, so they won't tip over and make a mess. Then pour the epson salt solution into the shells.

If you want brightly colored crystals, add a drop of food coloring. You might even try adding small drops of two or more colors to the same shell. Be sure to leave some of them uncolored, because I think the pure crystals are prettier than the colored ones.

Carefully place the egg carton into the refrigerator. Put it in a place where it will not be bumped or disturbed, and let it sit for at least 3 hours. That will give your crystals plenty of time to form.

Once you have plenty of crystals, remove the egg carton from the refrigerator. There will still be liquid in the shells, which you can carefully pour into the sink. Be careful not to let the crystals fall out of the shell as you drain them. Each shell should have a mass of needle-shaped crystals inside. As they dry, they will become even more bright and shiny.

You can play with the concentration of the epson salts. Adding more epson salts to the water will give you a denser cluster of crystals, while adding a bit less will give you a better view of the individual crystals. If you used clean egg shells, your crystals should remain bright and shiny for weeks.

To complete this unit, you will need these common, household items.

• several clear drinking glasses
• food coloring
• water
• a spoon for stirring
• a glass jar
• several pennies or a piece of copper pipe
• your fingernail
• an iron nail
• an unglazed porcelain tile
• table salt
• course or rock salt
• a magnifying glass
• a hammer
• colored tape, labels or dots for marking items. Office supply stores carry adhesive, colored dots that work perfectly for this.
• a disposable plastic or paper cup
• epsom salts
• a refrigerator
• paper towels
• orange juice
• a freezer
• a spoon

You will also need some mineral specimens to work with. I suggest at least four or five from the following list.

• quartz (crystal, milky, rose, amethyst, citrine)
• calcite
• gypsum
• pyrite
• galena
• hematite
• mica (muscovite, biotite)
• feldspar (plagioclase, orthoclase)
• fluorite
• corundum

You will find suggestions for sources of mineral specimens on the "First you need some specimens" page.

How can a random assortment of molecules arrange themselves in geometric shapes with such smooth sides and precise angles?

It has to do with how the molecules fit together. Imagine a jigsaw puzzle. You start with a pile of strangely shaped pieces, but when you put them together, you wind up with a rectangular shape, with smooth sides and sharp corners. No matter how many times you take it apart and put it back together, the puzzle will always form the same shape, with the same angles at the corners.

While molecules in a quartz crystal are not shaped like jigsaw pieces, they do fit together in a very specific way to form the crystal. A common example is a quartz crystal. A well formed quartz crystal has six sides, forming a hexagonal crystal that usually comes together at the end to form a point. The angles where those six sides meet will always be exactly 120°. It does not matter if the crystal is large or small, thick or thin, long or short. The flat parts of the crystal, called crystal faces, may be different sizes, producing crystals with different shapes, but the angles between those faces will still be 120°. If you have several quartz crystals, you can explore that for yourself.

You will need:

• several quartz crystals
• The printable Quartz Angle Sheet
• a printer
• a piece of stiff paper
• scissors

If you can't print the Quartz Angle Sheet, you will also need:

• a pen or pencil
• a protractor

Carefully cut out the Quartz Angle Sheet, being especially careful with the notch. If you can't print the sheet, cut a notch with an angle of exactly 120°. When you hold the notch against the crystal, it should fit perfectly with the angle between any of the six sides. This should work with any quartz crystal, no matter how large or how small the crystal is.

Note: It will not fit the angles from the crystal faces at the point. Those faces have different angles, which are also constant from one crystal to another.

Your $20/year subscription helps cover the costs of producing new videos, writing curriculum units, site development, and hosting. Without that support, this site would not be possible.

If you are already a subscriber, and having problems logging in, please check the Support Page.

If you are not yet a subscriber, please check out the Free Stuff page, and Subscribe Now.

Not all crystals form from dissolved chemicals. Some crystals start as liquids, such as magma (molten rock.) As the liquid cools and changes to a solid, it can form crystals. Just as wax freezes at a different temperature from water, different chemicals will crystalize at different temperatures, so some crystals form while other parts of the magma are still liquid. As the magma gets cooler and cooler, more and more minerals crystalize out. Want to see how a mixture of liquids can crystalize at different temperatures? You will need:

Your $20/year subscription helps cover the costs of producing new videos, writing curriculum units, site development, and hosting. Without that support, this site would not be possible.

If you are already a subscriber, and having problems logging in, please check the Support Page.

If you are not yet a subscriber, please check out the Free Stuff page, and Subscribe Now.

One way that crystals form is from chemicals dissolved in water. If the water gets cooler, dissolves other chemicals, or evaporates, some of the dissolved chemicals can be deposited as crystals. Often, growing crystals can be a fairly long, involved process, but with this activity, we will grow some nice crystals quickly and easily. To try this, you will need:

Your $20/year subscription helps cover the costs of producing new videos, writing curriculum units, site development, and hosting. Without that support, this site would not be possible.

If you are already a subscriber, and having problems logging in, please check the Support Page.

If you are not yet a subscriber, please check out the Free Stuff page, and Subscribe Now.

The beauty and precision of crystals leads many people to collect minerals. They look more like cut gemstones than something that was dug up out of the ground. Each mineral has one or more crystal forms, and those forms can be used to help identify the mineral.

Crystals form in two very different ways, and we will explore both by growing some crystals of our own.

Mineral name: There are so many minerals that are metal ores that I lumped them all into one group for this exercise.

Your $20/year subscription helps cover the costs of producing new videos, writing curriculum units, site development, and hosting. Without that support, this site would not be possible.

If you are already a subscriber, and having problems logging in, please check the Support Page.

If you are not yet a subscriber, please check out the Free Stuff page, and Subscribe Now.

Mineral name: Feldspars are a group of minerals made of aluminum, silicon, and oxygen. Examples include orthoclase, plagioclase, labradorite, and microcline.

Your $20/year subscription helps cover the costs of producing new videos, writing curriculum units, site development, and hosting. Without that support, this site would not be possible.

If you are already a subscriber, and having problems logging in, please check the Support Page.

If you are not yet a subscriber, please check out the Free Stuff page, and Subscribe Now.

Mineral name: Calcite

Your $20/year subscription helps cover the costs of producing new videos, writing curriculum units, site development, and hosting. Without that support, this site would not be possible.

If you are already a subscriber, and having problems logging in, please check the Support Page.

If you are not yet a subscriber, please check out the Free Stuff page, and Subscribe Now.