NAME _______________________________ LAB DAY _____________ GRADE _____________ MINERALS Atoms and Molecules An atom is the most basic unit of any type of chemical element; 92 types occur in nature. Atoms join together to form the molecules that make up the surface of the earth, the water that covers most of it, the atmosphere that surrounds it and the bodies of living organisms. Most of the earth’s crust is composed of only eight types of atoms. Almost half the atoms in the earth’s crust are oxygen atoms; another quarter of the crust is made of silicon, a major component of glass. The remaining six elements most abundant in the lithosphere are aluminum, iron, calcium, sodium, potassium, and magnesium. Not surprisingly, these elements are among those found in the bodies of living organisms as well. Minerals A mineral is a naturally occurring inorganic molecule that has a specific chemical composition and characteristic physical properties. The atoms that comprise them form a structure with a very regular, symmetrical, or “crystalline” arrangement. Minerals may be made of different types of atoms. Garnet, for example, is composed of magnesium, silicon, and oxygen. Some minerals, such as gold or silver, are made up of only one type of atom and are known as “native minerals.” You may recognize the names of some minerals: garnet, turquoise, emerald, diamond – all gemstones for which street in Pacific Beach are named. In a laboratory, chemical analyses are used to identify minerals, but naturalists are able to make fairly accurate identifications in the field from physical features of minerals such as color, luster, density, and hardness. Activity 1, you will examine some of these physical and chemical characteristics and then use what you have learned to identify some minerals. Rocks Rocks are formed from of minerals. Some are made of a single mineral. Limestone, for instance, is formed almost entirely of the mineral calcite. Other rocks are formed of combinations of minerals. The minerals that make up a rock retain their unique properties; the atoms are not chemically combined. Think of ice-­‐cream with nuts and chocolates mixed in – each component retains its distinct features. In Activity 2, you will learn about the different types of rocks and features that can be used to recognize each type. Rocks may be composed of different minerals. In addition, rocks can be form different rock types when subjected to extreme temperatures and/or pressure and other changes that cause them to be altered into a new type of rock entirely. Thus, there are two 1 factors that determine the type of rock: (1) the processes that formed it and (2) its mineral composition. 1. In your own words, explain what a mineral is. 2. What is meant by the term “native mineral?” 3. What is the relationship between a mineral and a rock? 4. What two factors determine rock type? Characteristics to help identify a mineral A. Features that can be used to help identify minerals in a natural setting outdoors (“in the field”) Minerals can be identified based on a number of physical characteristics that are easily observed in the field. You have a number of unidentified minerals displayed at your table which you will identify based on physical characteristics. Complete the table below for all of your specimens. Color 1. Which mineral(s) are the same, or very similar to eachother, in color? 2. Which mineral(s) have a very distinctive color and how would you describe the color? Luster Luster refers to the way something reflects light. There are many terms used by mineralogists to describe luster. Metallic -­‐ reflective like metal Vitreous -­‐ not metallic, but shiny, like slivers of broken glass Greasy -­‐ greasy appearance Waxy -­‐ somewhat dull luster, like the surface of a candle Earthy -­‐ completely dull, like clay 2
3. Which mineral(s), if any, have a metallic luster? 4. Which mineral(s), if any, have a vitreous luster? 5. Which mineral(s), if any, have a greasy luster? 6. Which mineral(s), if any, have a waxy luster? 7. Which mineral(s), if any, have an earthy luster? Feel Some minerals have a sharp or jagged feel, whereas others have a greasy or oily feel. 8. Which of the minerals has a sharp or jagged feel? 9. Which of the minerals has a greasy feel? Magnetism 10. Which of the minerals is magnetic? Cleavage When a mineral breaks it does so either by fracturing (no cleavage) or by cleaving. Cleavage refers to the tendency of crystalline materials to split along definite planes to form smooth surfaces. Types of cleavage include: Basal cleavage -­‐ occurs in one direction; the minerals splits apart like sheets of paper Cubic cleavage -­‐ occurs in two directions, at 90 degree angles, forming cubes Rhombohedral cleavage -­‐ occurs on two directions, forming rhomboids Cubic Cleavage Rhombohedral Cleavage 3 11. Identify a mineral that exhibits basal cleavage. 12. Identify a mineral that exhibits cubic cleavage. 13. Identify a mineral that exhibits rhombohedral cleavage. 14. Identify a mineral that fractures. Density Density refers to the weight of a given volume of substance. For example, a box full of lead weighs more than the same box full of Styrofoam, hence the lead is denser. Pick up the dark grey minerals that are very similar in color and, in some cases, similar in luster as well. 15. Which has the highest density? 16. Which has the lowest density? Hardness Diamonds are the hardest naturally occurring substances known and are useful in many industries as a result. Hardness can be measured on a scale known as the Mohs’ Scale, named for the German mineralogist Friedrich Mohs. The Mohs scale is based on the hardness of 10 common minerals ranging from the softest, talc (1) to the hardest, diamond (10). Minerals are then ranked compared to these 10 examples. The Mohs Scale does not reflect absolute hardness – a diamond is actually 1500 times as hard as talc! Several items have been provided for your use in determining physical properties, including copper penny (H=3), a nail (H=5), an unglazed porcelain streak plate (H=7.5). Try scratching each of these with the others to determine their relative hardnesses. Where does your fingernail fit into this hardness scale? A mineral will scratch any substance lower on the scale and will be scratched by any substance with a higher number. Most often we are able only to narrow down hardness to within a certain range; for example, if an unknown mineral scratches a copper penny but does not scratch a glass plate, its hardness must be greater than 3.0 and less than 5.5. Usually this range of values is sufficient to identify an unknown. 4
Do this with the specimens indicated by your instructor and complete the table below Mineral Hardness Streak Color Powdered minerals sometimes have a color that is different from what you observe when the mineral is intact. This can be determined by firmly streaking a sample of the mineral across a ceramic plate. Do this with the specimens indicated by your instructor and complete the table below Mineral Streak Color 17. Are any of the streak colors different than you would have predicted based on the mineral’s color? B. Features that can be used to help identify minerals in a laboratory setting Fluorescence – back room In some minerals, ultraviolet light 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 thermoluminescence. And there are some minerals that will glow when they are stuck or crushed; this is called triboluminescence. Go to the light box in the back room and look through the UV protective goggles at each of the specimens. 18. Which one of the three does not fluoresce? 19. Do all the others fluoresce in the same way? 20. Which specimen shows two colors under UV light? 5 Effervescence -­‐ in front of window (“Acid Test”) Minerals containing carbonate (C03) chemically react with acid to produce carbon dioxide (C02), the same substance that causes the bubbles when in soda. CAUTION – BURNS – HEED SAFETY NOTES Procedure: (1) Wear goggles and hold the test tube with the metal clamp. (2) Place a small scoop of powdered calcite in a test tube. (3) Add a few drops of dilute hydrochloric acid. Keep containers on their plastic drip trays! (4) When you have completed your observations, pour the excess hydrochloric acid into the waste container provided – not in the sink! (5) Rinse the test tube and place upside-­‐down in the second rack to dry. 21. What happened when calcite was treated with acid? 22. What are the bubbles are made of? Odor – in front of window Quite a few minerals have odors. The best known is probably sulfur, which produces a gas that smells like rotten eggs when heated. Minerals containing arsenic smell like garlic when they are heated. Determine if gypsum or iron pyrite have a characteristic odor when heated. Procedure: (1) Wear goggles and hold the test tube with the metal clamp. (2) Place a small scoop of powdered iron pyrite in a test tube, then place a foil splatter cap on the tube. (3) Heat over a bunsen burner until the sample just starts to smoke, then allow to cool enough to remove the cap. (4) Use the paper “fan” to waft the odor towards you. (5) When you have completed your observations, pour the excess mineral into the waste container provided – not in the sink! (6) Leave the test tube right side up in the second rack to cool completely. 23. How would you describe the odor of iron pyrite when heated? 24. What chemical element do you think iron pyrite probably contains? 6
NAME _______________________________ LAB DAY _____________ GRADE _____________ ROCKS A rock is a naturally formed mixture of minerals. Some minerals are readily visible in the rock, but others are too well mixed in to easily distinguish. Rocks are divided into three basic types, depending upon how they were formed: igneous, sedimentary, and metamorphic 1. In your own words, explain what a rock is. 2. Observe the minerals display at the start of the rocks section. Which 4 minerals make up most of our local igneous rock? IGNEOUS ROCKS Igneous rocks (from the Greek word for fire) form when hot, molten rock (magma) crystallizes and solidifies. Igneous rocks are divided into two groups: intrusive (plutonic) or extrusive, depending upon where the molten rock solidifies. INTRUSIVE IGNEOUS ROCK Intrusive, or plutonic, igneous rock forms when magma is trapped deep inside the Earth where it cools very slowly over many thousands or millions of years until it solidifies. 3. Based on color, which intrusive igneous rocks do you think contain lots of quartz or feldspar? 4. Based on color, which intrusive igneous rocks do you think contain lots of hornblende or biotite mica? 7 EXTRUSIVE IGNEOUS ROCK Extrusive, or volcanic, igneous rock is produced when magma exits and cools outside of, or very near the Earth’s surface. The magma, called lava when molten rock erupts on the surface, cools and solidifies almost instantly when it is exposed to the relatively cool temperature of the atmosphere. Quick cooling means that mineral crystals don't have much time to grow, so these rocks have a very fine-­‐grained or even glassy texture. Hot gas bubbles are often trapped in the quenched lava, forming a bubbly, vesicular texture. Basalt is a(n) __________ rock, while gabbro is a __________ rock. Basalt and gabbro have a similar composition, but look quite different. What makes rocks made of similar components look so different? What use was obsidian put to by stone age people? SEDIMENTARY ROCKS Sedimentary rocks are formed from pre-­‐existing rocks or pieces of once-­‐living organisms. They form from deposits that accumulate on the Earth’s surface. Sedimentary rocks often have distinctive layering or bedding. TYPES OF SEDIMENTARY ROCK INCLUDE: clastic organismic (biologic) chemical CLASTIC SEDIMENTARY ROCK Clastic sedimentary rock made up of pieces (clasts) of pre-­‐existing rocks. pieces of rock are loosened by weathering, then transported to some basin or depression where sediment is trapped. If the sediment is buried deeply, it becomes compacted and cemented, forming sedimentary rock. Particles range in size from microscopic clay to huge boulders. 5. ____________________ is made of sand-­‐sized clasts, whereas ____________________ is made of pebbles and larger rocks surrounded by a matrix of sand or mud. 6. Compare sandstone to conglomerate. What do they have in common that makes them both clastic sedimentary rocks? 8
ORGANISMIC (BIOLOGIC) SEDIMENTARY ROCK Organismic (biologic) sedimentary rocks form when large numbers of living things die, pile up, and their remaining hard parts are compressed and cemented to form rock. 7. Examine the display materials and indicate what organisms diatomite is made of. CHEMICAL SEDIMENTARY ROCK Chemical sedimentary rocks are formed by chemical precipitation. The stalactites and stalagmites you see in caves form this way, so does the rock salt that table salt comes from. This process begins when water traveling through rock dissolves some of the minerals, carrying them away from their source. Eventually these minerals can be redeposited, or precipitated, when the water evaporates away or when the water becomes over-­‐saturated with minerals. Sometimes you will see mineral deposits fromed on the end of a dripping faucett. 8. Why do the drops of water on your windshield leave a spot behind when they dry out? 9. All of the chemically formed rocks are similar in color. Why? (Hint: Do you think that all minerals dissolve equally well in water?) METAMORPHIC ROCKS Metamorphic rocks started out as some other type of rock, but have been substantially changed from their original igneous, sedimentary, or earlier metamorphic form. Metamorphic rocks form when rocks are subjected to high heat, high pressure, hot, mineral-­‐rich fluids or, more commonly, some combination of these factors. Conditions like these are found deep within the Earth or where tectonic plates meet. In metamorphic rocks some or all of the minerals in the original rock are replaced, atom by atom, by new minerals. Metamorphic rocks are often squished, smeared out, and folded. Despite these uncomfortable conditions, metamorphic rocks do not get hot enough to melt, or they would become igneous rocks! There are two major types of metamorphic rock: foliated and nonfoliated. Foliated metamorphic rocks develop a sheet-­‐like structure that reflects the direction in which pressure was applied. Slate, schist, and gneiss (pronounced 'nice') are all foliated metamorphic rocks. Non-­‐foliated metamorphic rocks do not have a sheet-­‐like structure. 10. Explain the difference between foliated and nonfoliated metamorphic rocks. 9 11. One of the rock specimens was under very high pressure and temperature to allow it to fold intensely without breaking. Which rock shows the strongest evidence of folding? . 12. What other rocks on display are foliated metamorphic rocks? (Refer back to the description.) 13. Give an example of a nonfoliated metamorphic rock on display. 14. Compare slate to shale. Slate is a __________ rock, while shale is a __________ rock. They are very similar with respect to color, but quite different with respect to ____________. Explain why this is so. 15. Which of the metamorphic rocks seems likely to have been produced by the metamorphosis of limestone? 16. Which of the metamorphic rocks seems likely to have been produced by the metamorphosis of Lava? 17. Which of the metamorphic rocks seems likely to have been produced by the metamorphosis of Sandstone? 10