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Rocks & Minerals
Teaching Tip: Rocks & Minerals 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. Minerals form a crystalline structure which gives rocks their "rough" texture. Rocks are mixtures, or aggregates, of different minerals. They are divided into three categories based on how different rocks are formed: igneous, sedimentary, and metamorphic. Igneous rocks are formed when hot magma from volcanoes is rapidly cooled, either by hitting underground air pockets or by flowing from the mouth of a volcano as lava. Granite, obsidian, and pumice are all common examples of igneous rocks. Sedimentary rocks are formed by layers of earth being mixed and compressed together for extended periods of time. Common examples of these rocks are limestone, sandstone, and shale. Metamorphic rocks are a combination of rock types, usually compressed together by high pressure, which tends to give them a more hard, grainy texture than the other two types. Schist, slate, and gneiss (pronounced like "nice") are metamorphic rocks. If you or your children are unfamiliar with what these rocks look like, you may want to examine at least one specimen from each category. Our basic set of 35 mounted rocks and minerals is ideal if you cannot find many specimens on your own. Also, if possible, compare two or more rocks per category, so that you can observe differences and similarities. For example, pumice has a very rough, porous surface and obsidian, another igneous rock, is very smooth and shiny. Teaching Tip: Gemstones When most people think of rocks, they think of the hard gray or brown objects that range in size from pebble to boulder. Have you ever been startled when you heard someone say, "Look at that rock!" when they saw a diamond ring? What can something so beautiful have to do with the gravel in the alley? The diamond, along with other beautiful stones, is classified as a gemstone. A gem or a gemstone is any mineral that can be cut and polished for jewelry or other decoration. The most precious gems are chosen for their beauty, rarity, and durability. Semi-precious gems usually have one or two of these characteristics, but fall short in some area. Fluorite, for instance, is very beautiful but it is too soft and will scratch easily. Diamonds are gemstones that are considered very precious, and for good reasons. The diamond is generally regarded as one of the most beautiful gemstones. It is relatively rare, because much diamond is not of jewelry quality. The average stone in an engagement ring is the product of the removal and processing of 200 to 400 million times its volume of rock. The diamond's strongest point, however, is its durability. It is the hardest substance found in nature, four times harder than the next hardest natural substance, corundum (Sapphire and Ruby). It also has the highest melting point, and conducts heat five times better than the second best element, silver. The diamond truly deserves the classification of "Precious Gemstone." While most gemstones are minerals, there is a small class called "Organic Gemstones." These gems are "organic" because they are formed as either a product or a part of a living organism. They are prized for their beauty and rarity, but they are not as durable as inorganic (mineral) gemstones. The pearl is an excellent example of an organic gemstone. It is formed when an irritant, such as a small grain of sand, gets into an oyster's shell. The oyster (or other mollusk) reacts by gradually coating the irritant with layers of nacre. Nacre is the substance called "mother of pearl" that lines the inside of the oyster's shell. Natural pearls are very rare, but a system has been developed whereby an irritant is deliberately placed inside the oyster's shell, causing it to begin forming a pearl. Pearls derived in this manner are called "cultured pearls." Our Rocks and Minerals deluxe set contains several organic and inorganic gemstones to examine: Petrified Wood, Agate, Jasper, Rose Quartz, and Corundum. Teaching Tip: Rock Collecting 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 encouraging your children to keep the interesting rocks they find on walks and hikes. You might want to wrap larger specimens in newspaper and put small ones in plastic baggies 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 with a local library. 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. Use a magnifying glass to observe different rocks and minerals. Magnification reveals much greater pattern and texture than your eyes can see unaided and can make even a dull brown rock fascinating to study! If you have a low-power stereo microscope, you can view even more detail than with the magnifying glass. Teaching Tip: Testing Rocks & Minerals There are many tests you can perform to help you identify your rock and mineral specimens. Our mineral test kit contains everything you will for these tests. 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. In the early 1800s, Friedrich Mohs used common minerals to invent a scale for comparing the hardness among rocks. 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. (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. 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. Noteworthy Scientist: Richard Kirwan (1733-1812) Richard Kirwan was born in County Galway, Ireland, in 1733. He received much of his education in France and began studying at the University of Poitiers when he was seventeen. In 1754 he begin a Jesuit novitiate but returned to Ireland the next year when his older brother--the heir to the family estate--died. After joining the evangelical state church, he spent a few years in the field of law, after which he turned to science. While living for a while in London, Kirwan joined the Royal Society--a group of men who were interested in science--and wrote a number of scholarly papers and books. In 1784, he wrote Elements in Mineralogy, the first systematic work on mineralogy (the study, classification, and identification of minerals). Kirwan moved to Dublin in 1787, where he helped to found the Royal Irish Society. He became the Society's president in 1799, holding that position until the time of his death. For several years Kirwan supported the phlogiston theory, the idea that a hypothetical substance called phlogiston caused burning. He wrote a book upholding this theory which was translated by the wife of a French scientist, Lavoisier. Lavoisier, who is now famous for showing that burning is caused by the presence of oxygen and not phlogiston, was allowed to include a word of warning as the preface to the book. Kirwan was later convinced that Lavoisier was correct and was not too proud to admit that he had been wrong about phlogiston. Kirwan made contributions to the fields of chemistry, mineralogy, and meteorology as well as wrote a book on logic. He also wrote a book supporting flood geology, the idea that most fossils were put in place by the biblical Flood. Fabulous Facts What's the difference? Did you know that rubies and sapphires are two varieties of the exact same mineral? A ruby is the red variety of the mineral Corundum, while sapphires are all the other varieties. Sapphires are often blue, but can be almost any color. Lead rings? Did you know that graphite (pencil lead) and diamonds are both made of the element Carbon? Though they are the same chemical compound, their structures and properties are very different. Diamond is the hardest natural substance, but graphite is very soft. Diamond is an excellent electrical insulator; graphite is a good conductor of electricity. Diamond is transparent, but graphite is opaque. They may be brothers, but they aren't identical twins! A glass rock? Obsidian, formed when lava is rapidly cooled, is a naturally-occurring glass. Obsidian is composed mostly of silica and has a very smooth texture because it does not have the crystalline structure that is usually formed by the presence of minerals. Obsidian is usually listed as an igneous rock, although it is not technically a "true" rock because it is not composed of mineral crystals. Obsidian was once used for making sharp spear and arrow heads. The Scientific Speaker Lapidary: A cutter, polisher, or engraver of precious stones. Science Links www.rockhoundingar.com Here is the authoritative guide to rock and mineral collecting. http://mineral.galleries.com/minerals/by-name.htm Browse through this fascinating site for pictures of minerals, ranging from common elements to precious stones! Includes detailed information about each mineral and the different classes of minerals. www.msha.gov/KIDS/MINING.HTM Visit this page to find out some of the main minerals that are mined in each of the fifty states. www.minsocam.org/MSA/K12/properties/minid/mineralid.html Use this site to help you identify your mineral specimens! NOTE: Home Science Tools does not necessarily agree with or endorse all opinions and information expressed on the sites listed in this newsletter. Please use at your discretion. |
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