Collecting rocks and minerals is a fun way to learn about geology! Most kids are naturally inclined to pick up any ‘pretty’ rock that they see, which provides a great learning opportunity. Start by keeping the interesting rocks you find on walks and hikes. You might want to wrap larger specimens in newspaper and put small ones in plastic ziplocks until you get home.
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.
Sort through the specimens that you’ve collected, putting similar stones together. Once you have done that, use a rocks and minerals guide and try to identify each rock. Match up color and description as best as possible. If you don’t have a good guide, check one out at a local library. Use the tests in the next section for more properties that will help you identify a rock or mineral.
As you identify each specimen, make a label for it. If possible, write down the location and the date when the rock or mineral was collected. For rocks, you might also want to 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, Galena is PbS (lead sulfide).
Keep your specimens in a compartmentalized box or in cardboard egg cartons. If you want to number your specimens, use a permanent marker to mark each one consecutively. Write the number on each label as well. That way you won’t worry about getting the rocks confused with each other.
Identifying Specimens: Testing Rocks & Minerals
There are many tests you can perform to help you identify your rock and mineral specimens. The first step is to examine your specimen with a magnifying glass and take note of its outside appearance. Look for the mineral’s transparency. If you can see through the specimen, it is transparent. If light can pass through, but the specimen cannot be seen through, your mineral is translucent. Minerals that do not let light through are called opaque.
Next, test your specimen 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 the penny but not with your fingernail, it has a hardness between 2.5 and 3.5. Also try scratching your specimen with another rock to see which one is harder.
One last 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.