Lab9new - Name SID Lab 9 Igneous Rocks G J P and S Ch 4...

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Name: SID: Lab 9: Igneous Rocks G. J. P. and S., Ch 4 Introduction: In the previous lab we learned about mineral characteristics, properties, and identities as well as the three basic rock types (igneous, sedimentary and metamorphic). Today we will explore the basic classification scheme for igneous rocks, based on texture and silica content. We will also investigate the relationships between igneous rock types and tectonic settings. Throughout the lab, remember that – in spite of our tables of characteristics and rock classifications - the diversity of rock in nature is generally continuous. Objectives: Observation of various igneous rocks to determine their characteristic minerals and properties, and interpret their origins. By the end of the period you should be able to identify, group, and classify the major types of igneous rocks, understand which geologic proceses they imply, and be familiar with some of the manifestations of these processes in California. Answers: Please answer the indented, numbered questions on the answer sheet at the back of the lab handout . Explanations should be concise; most questions can be answered with a few words, or a sentence or two. All answers should be your own, but we encourage you to discuss and check your answers with 2-3 other students. Discussion and explanation are terrific ways to learn! Labs are graded out of 100 points, and then scaled accordingly. -------------------------------------------------------------------------------------------------------------- Basic Observations (3 pts) 1) Examine the following map and write down at least three observations you can make about this map and the distribution of volcanism. 1
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Part 1 : Identifying Igneous Rocks There are many rock types in nature, many more than are given in the simplified classification tables that are common to geology. Get into the habit of justifying why you call a rock a certain name. It is easy to be fooled by a rock if you do not train yourself to make careful observations. Basic observation provides you with a context and an intuitive understanding, poses specific directions for questioning, and determines where you may start to look for answers. In practice, these initial observations are later complimented by a detailed microscopic and/or chemical analysis of the rock to make an unequivocal identification. All igneous rocks are classified by the types of minerals present, resultant chemistry, and by the sizes of their crystals . While the minerals reflect the chemistry of the original magmas, the sizes and shapes of the crystals (the rock’s texture) indicate how long it took for the magma to cool. Texture is used to subdivide igneous rocks into two major groups: Intrusive or plutonic rocks, such as granite, have crystals large enough to be seen with the naked eye, indicating a slowly cooling magma that solidified within the Earth’s crust; extrusive or volcanic rocks usually have some (or all) microscopic crystals because the magma cooled very quickly when exposed to cool air (or water) on the surface of the Earth. This is
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