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Advance Placement Rocks and Minerals: Classification and Usage Rocks and Minerals Objectives Materials Introduction After this lab you should be able to do the following: - Understand and perform different methods of classifying rocks and minerals. - Identify important common rocks and minerals. - Identify common uses of rocks and minerals. Materials for this lab are: Mineral dichotomous keys Mineral Samples Glass plate steel nail Copper penny magnet Hand lens hydrochloric acid Internet Streak Plates Rock samples Water Gloves First, before we begin, we must understand what a mineral is. A mineral is a naturally occurring, inorganic, solid, with a definite chemical composition and crystal structure. Now that you understand what a mineral is, lets discuss the methods we can use to identify them. Minerals have certain physical properties (characteristics) that help us to identify them, such as: Color Although color is the most obvious, it is the least reliable. For example specimens of the mineral- calcite are always the same color as Sulfur, and Pyrite. Streak When an unknown mineral is rubbed against a piece of unglazed porcelain (a.k.a.-streak plate) it may produce a colored line. This color will help to determine the minerals identification. This test is very useful for Hematite and Limonite. Many times a sample does not leave a color streak however, or is harder than the streak plate. Examples are the minerals Galena and Hematite. Both have metallic luster and seem heavy for their relative sizes, but Hematite has a red brown streak. Fracture and Cleavage These terms describe the way a mineral breaks. If a mineral fractures, it breaks along rough edges. If it cleaves, then it breaks along smooth, flat surfaces. Some rocks also have a type of cleavage called slaty cleavage. This is not the same type of cleavage exhibited by a mineral. Cleavage found in minerals is the result of the way the chemicals bond together, but in rocks, it is the result of the way the minerals align themselves parallel to one another. When some minerals fracture, they appear to break along long curved surfaces (that look like a shell. This type of fracture is known as conchoidal fracture and Quartz and the igneous rock Obsidian will demonstrate this type of fracture. The rough, irregular breaking is known as hackly fracture. Hardness This is how resistant a mineral is to being scratched. We use the Mohs scale to classify a given minerals hardness. If we have a sample that we can scratch with Fluorite, but not with Gypsum, we can predict that the samples hardness is around 3. But if you forgot your hardness scale minerals at home (and don't we all sometimes) we can use a simple field method. The technique used is rather similar. All you do is try to scratch the unknown mineral with various items, such as a fingernail (hardness of about 2.5), a penny (3), a steel nail (5.5) and a steel file (7). The item that first scratches the unknown is harder than the unknown so now you must estimate. Below is the Mohs Scale. MOHS SCALE OF HARDNESS MINERAL HARDNESS TALC 1 GYPSUM 2 CALCITE 3 FLUORITE 4 APATITE 5 FELDSPAR 6 QUARTZ 7 TOPAZ 8 CORUNDUM 9 DIAMOND 10 Luster The way a mineral reflects light. Does your mineral appear to be a metal (metallic luster)? Or does it look like a nonmetal (nonmetallic luster)? There are several other words used to describe luster. Crystal form The way the outside of this mineral looks is an expression of the arrangement of its atoms. This external expression is known as a crystal. Its crystal structure is the result of regular grouping of atoms that are homogeneous (having the same characteristics throughout the crystal). A crystal is a polyhedral form, which means it is a geometric solid. It has a specific set of faces, corners and edges, which is consistent with the geometric packing of the atoms. There are 6 basic crystal forms. The form that the unknown demonstrates is a good clue to its identity. Taste This will quickly identify the mineral halite (salt). If you are new to this process you must use this one with caution, as you never know what the unknown may be. Often, you may need to resort to this method (until you more fully understand other identifying traits) to differentiate halite from calcite. You should not use taste unless directed to by someone with higher knowledge Specific Gravity This characteristic relates to the minerals density. If the mineral is heavy for its size, then it has a high specific gravity. Water displacement is useful in determining specific gravity. Magnetism Is a mineral magnetic (try using a compass), or is it attracted by a magnet? This property is characteristic of Magnetite. Effervescence When some minerals are exposed to acids, they begin to fizz. This is a great method you can use to identify the mineral calcite. You can also use this one to detect the presence of calcite in rocks. Birefringence This is also known as double refraction. Birefringent minerals split the light into two different rays which gives the illusion of double vision in this Iceland Spar Calcite Fluorescence Some minerals display what is called the phenomenon of photoluminescence. This basically means that they "glow" when exposed to UV light (black light). The above mineral (opal) is demonstrating fluorescence. Also, the mineral Fluorite is often strongly fluorescent. Pre-lab Questions 1. Create a list of minerals you know we use. 2. Research quality of precious metals (gold, silver, copper) what useful properties do they show? 3. Choose three useful properties of minerals from above. In your own words, explain what you would look for to classify each property. Procedure 1. You will be provided with 12 sample minerals. Use the properties in the pre-lab to classify the properties of each minerals. Fill in a chart showing your results. 2. Two similar looking minerals from your twelve will be provided. Use the properties from above classify each. Explain how you were able to recognize the difference. Lab Questions 1. For each type of rock, describe how it forms and name an example. Also give the mineral make-up of that specific rock. Clastic sedimentary Biological sedimentary Chemical sedimentary Intrusive igneous Extrusive igneous Metamorphic 2. Use books or the internet to research uses of each of the following rocks and minerals. Identify each as a rock or a mineral. - Barite - Marble - Calcite - Mica - Coal - Molybdenum - Copper - Potash - Fluorite - Sandstone - Gypsum - Silver - Granite - Sulfur - Halite - Talc - Iron - Trona - Limestone - Ulexite 3. Use the internet to find the mineral(s) important to the following industries - automobile - cosmetics - fireworks 4. What are some reasons that mineral resources are considered valuable. 5. In North Carolina, the following rocks and minerals are mined: Gemstones - Emeralds, rubies, garnets and more than 300 other varieties, Gold, Crushed stone (aggregate), Kaolin clay, Olivine, Quartz and feldspar, Peat, Phosphate, Silica sand and quartz, Spodumene, Talc and pyrophyllite. Use the information you’ve collected to name three industries that would rely on North Carolina’s minerals.