Recommended Group Size: Groups of 2-3 This is a wet experiment and should ideally be done in the Science Lab

Transcription

1 Grade: 3rd Activity #: 1 Activity Title: Studying Rocks and Minerals Recommended Group Size: Groups of 2-3 Special Notes: This is a wet experiment and should ideally be done in the Science Lab Purpose Students will learn the difference between rocks and minerals. They will learn some of the ways of identifying minerals. They will learn the different types of rocks and learn what the Rock Cycle is. Students will test hardness, magnetic test, perform streak test and acid test on several mineral samples. They will also taste salt samples. Equipment (An asterisks (*) indicates that an item is provided in the Learning Lab.) Rock samples* Vinegar* Magnets* Steel nail* Copper penny (before 1981) Rock salt * Glass plate* Crushed chalk* Droppers* Instructions 1. Write the name of your rock/mineral specimen. Describe your rock samples. Write your answers on Table Run magnets along your rock samples. Are your samples magnetic? Write Yes or No in Table Test the hardness of your mineral specimen by conducting a scratch test. Use the following objects: your fingernail, a copper penny, a steel nail, and a glass plate. Write Yes or No in the boxes in Table 2. Write the Mohs scale number in the last column. 4. Streak Test: Predict what color streak each of the mineral specimens will leave. Then test your specimens on the streak plates. Write your observations on

2 Table 3. Some colors you will observe are greenish black, gray, white and colorless. 5. Acid test: Perform the acid test. Place one to two drops of vinegar on your mineral specimens and record what happens. Possible observations will include no reaction, bubbles formed, and dissolved. Then perform a test on the crushed chalk sample. Record your observations in Table Taste the rock salt samples. DO NOT TASTE THE OTHER SAMPLES! Suggested Discussion Topics WHAT IS THE DIFFERENCE BETWEEN A ROCK AND A MINERAL? A Rock is made up of one or more minerals. There are 3 types of rocks. They are Igneous Rocks, Sedimentary Rocks, and Metamorphic Rocks. We ll discuss these more later. A mineral is a naturally occurring, inorganic, solid which possesses a characteristic internal atomic structure and a definite chemical composition. Minerals must occur naturally. This means man-made substances such as steel would not be considered to be minerals. Inorganic substances are those substances that are not living and are not formed by living processes. Minerals will have definite chemical compositions, but these compositions may vary within given limits. Minerals will have distinctive physical properties such as color, cleavage, luster, streak, etc. MINERALS: How do we identify a mineral? Color - The color of a mineral is the first thing most people notice. But it can also be the least useful in identifying a mineral. Most minerals occur in more than one color. The other properties, such as hardness, cleavage, and luster, must be used instead. For some minerals, color can be characteristic and serve as a means of identification. Malichite is always green, azurite is always blue, and rhondonite is always red or pink. Streak - The streak of a mineral is the color of the powder left on a streak plate (piece of unglazed porcelain) when the mineral is scraped across it. The streak plate has a hardness of glass, so minerals with a Mohs Hardness >7 will scratch the streak plate and won't powder the mineral. Streak can be useful

3 for identifying metallic and earthy minerals. Nonmetallic minerals usually give a white streak because they are very light-colored. Other minerals may have very distinctive streaks; hematite, for example, always gives a reddish brown streak. Luster - Luster refers to how light is reflected from the surface of a mineral. The two main types of luster are metallic (like a quarter, silvery) and nonmetallic (like a dollar bill). Cleavage - The ability of a mineral to break along preferred planes. Certain planes of weakness exist in some minerals because of their particular atomic structure. Atomic bonds may be weaker in some directions than in others, so the mineral will tend to break, or cleave, in that direction. Minerals may have cleavage in only one direction, in only two directions, or in three or more directions. The cleavage angles at which these planes intersect may be distinctive. Hardness - The hardness of a mineral is its ability to resist scratching. Friedrich Mohs, a German mineralogist, developed a hardness scale over 100 years ago. The hardest mineral known, diamond, was assigned the number 10. The Mohs Hardness Scale ranks the order of hardness of minerals and some common objects. For example, your fingernail can scratch the minerals talc and gypsum, with a hardness of 2 or lower. A copper penny can scratch calcite, gypsum, and talc. A common misunderstanding of how to identify a diamond is that it will scratch glass. While this is true, other minerals can scratch glass, too, as long as they have a hardness >6. HARDNESS SCALE INDEX MINERAL COMMON OBJECTS 1 Talc 2 Gypsum Fingernail 3 Calcite 4 Fluorite Copper Penny 5 Apatite 6 Orthoclase 7 Quartz Glass 8 Topaz 9 Corundum 10 Diamond

4 Light/Heat - There are several ways that minerals can emit light. Some of these ways involve special lamps that emit non-visible ultraviolet light (at least not visible to humans). The light from these ultraviolet lamps reacts with the chemicals of a mineral and causes the mineral to glow; this is called fluorescence. If the mineral continues to glow after the light has been removed, this is called phosphorescence. Some minerals will glow when heated; this is called thermo-luminescence. Smell - Some minerals do have odors! Generally the odor is not strong. The smelliest mineral is sulfur. Odor is a fairly uncommon property in minerals and not reliable in general. Touch - Minerals that have a distinctive feel are generally low in hardness, but not always. Several metallic minerals such as copper have a jagged feel due to minute, sharp protrusions. Minerals such as graphite, talc and several other clay minerals have a greasy or oily feel. At times feel can distinguish two minerals. Solubility (water and acid) - Minerals do dissolve. Pure water can dissolve any mineral, at least partially. However most minerals do not dissolve in water fast enough that we can detect in a short period of time. The ones that do dissolve rapidly are therefore considered soluble and this can be diagnostic. Solubility is not just limited to water. Many acids are capable of dissolving minerals where water has no effect. Of course, identification of minerals using solubility is a test that could destroy the specimen, if it is soluble. An unneeded fragment can be used for such tests. Inclusions in Minerals - Many minerals have crystals of other minerals, air, water, tar, petroleum, rocks and in the case of amber, even animals included in their interiors. They are called, appropriately enough, inclusions. ROCKS Rocks are the most common material on Earth. They are naturally occurring combinations of one or more minerals. There are three main classes of Rocks. They are classified according to how they originated. Igneous rocks form from cooling bodies of magma. Magma is the term for liquid or melted rock and is usually quite hot. When magma flows onto the surface of the Earth from a volcano, it is called lava. When the lava cools

5 and forms a rock, that rock is an igneous rock. But there are also rocks that form from magma that does not reach the surface of the Earth. These two types of igneous rocks are called extrusive or volcanic (because it extruded or came out of the Earth in a volcano) and intrusive or plutonic (because it intruded and stayed inside the Earth). Sedimentary rocks are formed by the accumulation and subsequent reformation of sediments (broken down pieces of all 3 kinds of rocks caused by weathering, erosion and/or chemical breakdown). Water is always a key component in sedimentary rocks. Where there is water, there are sedimentary rocks being formed? Another common factor to sedimentary rocks is that they originate on the surface of the Earth, unlike most igneous and metamorphic rocks which originate in the interior of the Earth's crust. Metamorphic rocks are formed from older "parent" rock (either igneous or sedimentary) under intense heat and/or pressure at considerable depths beneath the earth's surface. Primordial rocks (minor class of rocks) are those that initially formed in outer space as the solar system (sun and planets) formed. These objects became comets, asteroids, meteoroids, and ultimately the planets. When they broke apart and hit the Earth, they became Primordial rocks. ROCK CYCLE Over time, various weathering processes erode igneous rocks and these rocks and the resulting particles or chemicals settle into beds and are compressed and cemented into sedimentary rocks. If these rocks are buried, heated and highly compressed they will be made into metamorphic rocks. If these rocks continue to be heated and compressed to the point that they melt, then the molten rock might eventually form another igneous rock. This is called the Rock Cycle. The rock cycle is an illustration that is used to explain how the three rock types are related to each other and how Earth processes change a rock from one type to another through geologic time. Plate tectonic movement is responsible for the recycling of rock materials and is the driving force of the rock cycle. It forms a complete circle as one rock can be turned into another.

6 HOW DO WE USE ROCKS AND MINERALS? Everything we do involves rocks and minerals and the metals we extract from them. It is estimated that you - and every other person in the United States - will use more than a million pounds of rocks, minerals and metals during your lifetime including: lead - used in the construction of batteries, as a radiation shielding during x-ray treatment by your doctor and dentist and as a protective shield on your TV screen to protect you from radiation. zinc - used as a rust inhibitor for steel in cars, buildings, bridges, ships and trains. copper - used in the manufacture of copper wire to conduct electricity needed in your car, home, office, school, church, appliances. aluminum - Cans, aircraft and automobile construction, sporting and electronic equipment, appliances. iron - Used to make steel for cars, subways, ships, cans, building construction, heavy equipment, appliances and towers. clays - Used to coat the pages of newspapers, magazines, stationery, brochures and boxes so that the ink used in printing on them will be bright and will not run. Also used as a brightener and abrasive in toothpaste and to provide a smooth coating for your stomach in medicines. salt - Used in food preservation (almost all canned and frozen food contain salt), to enhance the taste of foods, and to melt the ice on streets and during the winter. stone, sand, gravel and cement - Use in streets, highways and sidewalks; in the foundation for your house and school; as decorative materials for yards and gardens; in water purification plants to protect your health and in the construction of buildings from the smallest homes to the tallest buildings Minerals in Your Bedroom Hematite: hinges, handles, mattress springs Chromite: chrome plating on bed Quartz : mirror Graphite, Galena, Sphalerite : Batteries Brass (an alloy of copper and zinc): base of lamp Quartz: light bulb Wolframite: lamp filament Copper: lamp wiring

7 Minerals in your bathroom Fluorite: toothpaste Gold: fillings, Cinnabar: fillings Feldspar: porcelain toilet Chromite: plumbing fixtures, Copper: tubing on toilet Borax: abrasive, cleaner, and antiseptic Minerals in your kitchen Quartz: drinking glasses Hematite, Chromite, Galena, Copper, Quartz: Dishwasher Hematite, Chromite: stainless steel Galena, Copper, Cinnabar: thermometer Pentlandite: - Fridge Halite: table salt Additional Resources

8 Rock Experiment Lab Sheet Name Date Table 1. Sample Description Specimen # and Name Description Magnetic Table 2. Scratch Test/Hardness Test Results Specimen is scratched by Scratches glass Mohs Scale number Fingernail Penny nail

9 Mohs Scale of Hardness Mohs Scale Number 1 2 Common Tests Scratched by fingernail 3 Scratched by copper penny Scratched by steel nail Scratches glass 9 10 Scratches all common materials Table 3. Streak Test Results Specimen Predictions Observations Table 4. Acid Test Results Specimen Predictions Observations