What better way to study the earth than by going on a rock hound expedition? This hands-on exploration is a great way to get outside this summer, have some fun, and hopefully find some great rock specimens!
Rocks & Minerals 101
Each rock is different - some are smooth and round, some are sharp and dangerous. They come in all colors: pink, green, orange, white, red. Rocks can be found everywhere - from the backyard and driveway to high peaks or underground tunnels. Sometimes those shiny rocks we find aren't really rocks at all, but minerals like quartz.
Minerals are naturally-occurring, solid substances composed of chemical elements. This means that minerals, ranging from salt to rubies, are made up from the elements that appear on a periodic table. They are inorganic, not living or made up of living things.
Rocks are mixtures, or aggregates, of one or more minerals, and may also contain sediments such as soil, sand, or pebbles. Rocks are divided into three categories based on how they are formed: igneous, sedimentary, and metamorphic.
For an afternoon filled with fun why not bring the whole family or a few friends on a rock collecting adventure? A parent or adult should come along to drive to the destination, and look out for the safety of the group. Plus, having more people means a better chance of finding some really interesting rocks and minerals.
You can find a variety of rocks wherever you live, if you know where to look. The best places to be a rock hound are where natural bedrock is exposed, like a cliff or outcrop of rock. Fields may have rock outcroppings, but it will be easier to find rocks and minerals in a low place (a valley) or high place (mountain or cliff). If there are no rocky valleys or hills nearby, you could try looking at the edge of a river or stream. Or if you are near the ocean, try visiting a rocky shoreline. (Even a sandy beach has rocks, though: if you ever look closely at grains of sand, you'll see that it is really ground up bits of rock!)
If the location you choose is on private property, be sure to ask for permission from the owner first. If it is on government property, check with your state land department or Forest Services, to make sure it is okay to take away rock samples. It is illegal to collect rocks from national parks. Never try to collect rocks in tunnels or mines. It's a good idea to wear a hard hat if you're working under overhanging rock, and be sure that someone always knows where you are.
No matter where you go, finding enough rocks and minerals to make a really good collection will take time and patience. A rock hound is always on the lookout for interesting specimens to add to their collection!
If you see a rock that interests you, but it is too big to carry, use a rock pick to take off a smaller chunk. Be sure to wear safety goggles while using the pick. Try to find a piece that best represents what the larger sample is like. Does it have a colored pattern? Does it have layers of different colors or shiny crystals in it? Sometimes plain-looking rocks called geodes will have beautiful mineral crystal deposits inside; you can use a rock pick to break them open and see the crystals. When you have a specimen, put it in a plastic bag along with a note saying where you found it. Wrap up larger rocks, or ones with sharp points, in newspaper.
Before you leave, pack the tools you'll need to collect rocks and minerals, as well as the safety equipment that is necessary. Don't forget to pack a first-aid kit - some rocks have sharp edges, and you need to be prepared in case something happens.
>> See our handy guide to know just what to bring on the trip!
Before comparing what you found to the rocks and minerals in a guide book, clean off the specimens you've collected. You can use a brush (old toothbrushes work well) to 'clean' your specimens: brush the dirt off carefully, so that fragile rocks or minerals are not damaged. After they are clean, you can observe your specimens carefully and perform several tests to help identify them. (You can even get a mineral test kit, if you want.)
To identify a rock, look closely at the grain - is it coarse, fine, or in between? Use a magnifying glass, or look at it under a stereo microscope to see better detail. Is the rock or mineral transparent (you can see through it), translucent (it lets a little light through), or opaque (doesn't let any light through)? How would you describe the surface of the specimen? Do parts of it look waxy, pearly, glassy, or earthy and dull? All of these questions will help you correctly identify what kind of rock or mineral it is. Many specimens you may find will have layers of different colors - it is possible those represent different types of rock or mineral in the same sample.
One way to identify minerals is to test for hardness. Mineral hardness is measured on the Mohs Hardness Scale. On each level of the scale a mineral can be scratched by something of the same or higher level, but nothing lower. Number one on the Mohs scale is talc, because it is soft and very easy to scratch. Number ten is the diamond, because it is the hardest natural substance and can only be scratched by another diamond. Test your mineral specimen by trying to scratch it with your fingernail. Next try a copper penny, and then a steel nail. A fingernail has a hardness of 2.5, a penny is 3.5, and a steel nail is 5.5. If you are able to scratch your specimen with your fingernail but not with the penny, it has a hardness between 2.5 and 3.5. Also try scratching your specimen with another rock to see which one is harder. Remember that some of your rock specimens are made of more than one type of mineral, so different parts may have different hardness levels.
Another test that is commonly used is called a streak test. A mineral's 'streak,' or color when it is finely powdered, is always the same, even when the color of the mineral varies. (Sometime the streak can be very different from the color of the mineral itself.) Rub your specimen across a piece of porcelain tile (called a streak plate) and examine the color it leaves behind. You can also rub it across smooth cement if you don't have a tile.
Once you have performed your tests, compare your results with a rocks and minerals field guide to come to a final identification of your specimen. If you don't have a good guide, check your local library, or go here for an online rock identification guide of most commonly found specimens.
As a rock hound, you'll want to organize and protect the specimens you have found. Find a container, or several different-sized ones, to put your complete collection in. Keep in mind that this collection will be growing as you find more specimens, so leave some room. Egg cartons work well to keep minerals separate, or you could also buy an inexpensive display case. You may also consider making a display case using something like a gift box and some cardboard dividers to separate your specimens.
Before you assemble your collection, think about how to organize it. You could sort by color and size, or separate rocks from minerals and sort by igneous, metamorphic, or sedimentary, with minerals sorted according to hardness.
As you identify each rock or mineral, make an identification card on paper or cardstock. Index cards work well. Make sure that the card includes the mineral or rock's name, special features (such as color or hardness) where you found it, and when. For rocks, you can note information such as what minerals it is made of and whether it is igneous, sedimentary, or metamorphic. For minerals, note the elements that they are composed of: for example, the mineral Galena is composed of PbS (lead sulfide).
Label the rock by writing a number directly on the surface with a permanent marker. For darker rocks, you can paint a small square for a label, let it dry, then mark the number. For small rocks, you can glue a paper backing on, and write the number there. The identification card you made should have a corresponding number, so you can look up information easily. To keep the different identification cards organized, place them in a small binder or an index card holder.
Another fun thing to do with your collection is to use a rock tumbler to polish your finds. Polished rocks can be used for decoration or for jewelry-making.
On your rock hounding adventures, be sure to look carefully at your specimens for fossils! You might be able to see imprints of shells, leaves, or small animals in some of the rocks you find. When animals or plants are rapidly buried in layers of mud during a natural catastrophe, their bodies are protected from normal processes of decay: scavengers, bacteria, and chemicals are prevented from breaking down their bodies at the usual rate. The hard parts of the animals (such as their bones, teeth, and shells) are eventually replaced with minerals from the mud, which turn them into rock. The soft parts of the specimen, such as the scales of a fish or the leaves of a plant, sometimes leave a colored imprint in rock before they eventually decay. Trees or other organic matter that are covered with silica-rich water become petrified--they turn into solid mineral. All of these methods result in what we know as fossils.
A paleontologist is a scientist who studies fossils to find out more about extinct species or about any species that are evident in the fossil record. Fossils are most commonly found in limestone, shale, and sandstone, all relatively soft rock that erodes more easily than most rocks do. As the rock gradually wears away, the fossil layers within it are exposed.
Check out the beautiful pictures of rocks and minerals that the Smithsonian has recently acquired.
Find out how rocks are formed with this rock cycle animation.
Use this online interactive identification guide to help you identify your finds.