Are you a rock hound? Or maybe just a pebble puppy? If you're interested in rocks and minerals at all, you may like to collect and identify some. Rock and mineral collections are great for science projects. You can find rocks in your back yard, at the seashore, or along rivers and streams. Make sure you have permission to collect. You may not be permitted to collect rocks on public land. Ask at quarries to see if there are interesting rocks they will let you have. Some garden centers supply landscaping rock, and may let you take home chips that have broken off. Even mortuary supply companies can be helpful. They can often supply you with chips of marble, granite, or other stones that they use in making headstones.
What's the difference between rocks and minerals? Minerals are the materials that rocks are made out of. Minerals are crystals of pure or nearly pure compounds. Rocks are made up of crystals or particles of many kinds of minerals.
As you get started in rock hounding, try some of these projects to learn more about the rocks and minerals you find:
MINERAL IDENTIFICATION KIT
The cornerstone of your kit is a good rock and mineral identification book. The book will be more useful to you if you can identify two qualities of your minerals: hardness and streak color.
With some household items, you can test the approximate hardness of minerals. You'll need a penny, a steel knife or file, and a piece of glass. These can be used to test the hardness of minerals on a scale of 1 to 10:
1-2: a fingernail can scratch the mineral
3: a penny can scratch the mineral
4-5: the knife or file can scratch the mineral
7: the mineral can scratch the file and the glass
8-10: harder than most common minerals
Also put a piece of unglazed tile in your test kit. Many mineral identification books will tell you the streak color of a mineral. This is the color of the streak left behind when the mineral is rubbed on the tile.
In addition to hardness test equipment, a small bottle of vinegar can come in handy. Any rock containing the mineral calcium carbonate will bubble when vinegar is dropped on it. To try this out break a small piece off of a stick of chalk and put it in a cup. Pour some vinegar over it. Let it sit a few minutes and watch for bubbles. It won't fizz as vigorously as a mixture of baking soda and vinegar, but it will produce bubbles. Try some eggshells or small seashells in vinegar, since they're also made of calcium carbonate.
HOW CRYSTALS ARE FORMED
Mineral crystals are formed in several different ways. Some form when lava, which is molten rock, slowly cools. The slower the rock cools, the larger the crystals are that form. Lava that cools at the surface makes rocks such as basalt, which has such tiny crystals that they can only be seen with very powerful microscopes. Magma, or underground lava, cools very slowly and forms rocks such as granite, with visible crystals.
Crystals also form when water dissolves minerals and seeps into spaces in the earth. As the water evaporates or seeps away, the minerals left behind may form crystals. Geodes - hollow rocks with crystals inside - stalagmites, and stalactites are all formed when water leaves minerals behind.
Geode formation can be demonstrated with eggshells. Crack open an egg and save the insides for cooking. Wash the egg out, remove the membrane, and let the shell dry. Set the shell in an egg carton to steady it while you work. Pour about 1/4 cup of hot water in a jar and add any one of these chemicals to the jar: Epsom salts, borax, washing soda, baking soda, table salt, alum, cream of tartar, citric acid. Add enough of the chemical that you can't dissolve any more in the water. Pour the water into the eggshell. Fill other eggshells with other chemical solutions. Set the shells someplace where they won't be disturbed and leave them until the water evaporates completely. You'll soon have a homemade "geode" with beautiful crystals inside.
STALAGMITES AND STALACTITES
To demonstrate how stalagmites and stalactites form, you'll need two jars, some Epsom salts, and a piece of thick cotton string. Fill the jars with hot water and stir in Epsom salts until no more will dissolve. Tie small weights, such as washers, to each end of the string. Wet the string in the Epsom salt solution, and drop one weighted end in each jar. Let the middle of the string bow slightly. Place a plastic plate between the jars. As the solution evaporates from the string, more will creep up the string. Some will drip from the string and fall on the plate. The salts will form crystals hanging from the string and mounding up on the plate. Can you grow them long enough that your "stalagmite" and "stalactite" meet?
MAKE A SEDIMENTARY ROCK
Sedimentation is part of the rock cycle. Molten lava cools and forms igneous rocks, which weather away. Small particles of weathered rocks are deposited in sediments in lakes, bays, and oceans. Over time, the sediments compress, forming sedimentary rock.
You can demonstrate this with a 16 oz soda bottle. Cut away the neck and shoulders of the bottle with a pair of scissors. Mix together some sediment-like material with different particle sizes, such as sand and clay soil. Put about two inches of this mixture in the bottom of your bottle. Add enough water to cover it by an inch or two. Put your hand over the top of the bottle and shake until the particles are completely mixed with the water. Set the bottle aside where it won't be disturbed and let the water evaporate completely. This may take a week or so. When the sediments are completely dry, cut away the bottle and examine the layers. If there's enough clay in the mixture, it may be quite solid. Larger, sandier particle may have settled to the bottom, where the mixture may be more crumbly.
Many areas of the world have streams that have yielded at least a few gold particles. Ask the local Forest Service, Bureau of Land Management, or other public land agency where you might go to pan for gold.
If you don't have a gold pan, take a tin pie plate with you. You'll also need a pair of tweezers, a magnet, and a small vial to hold any gold flecks you find. Find a stream where the bottom is sandy. Scoop a handful of sand in your pan and add water. Swirl the sand around in the pan. Let the lighter sand spill over the edge of the pan while the heavier particles, such as gold, sink to the bottom. When all you have left in the pan is dark, iron-rich particles, pour out the water and look closely. If you're lucky, you may see tiny flecks of gold in the sand. Use tweezers to pick out the particles and put them in the vial. Don't worry if there's dark sand with it. Later, let your findings dry on a piece of paper and use the magnet to remove the iron particles, leaving the gold flecks behind. You many not strike it rich, but you may have enough to show off at school!