Refers to the minerals or components that make up the

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refers to the minerals or components that make up the rock, which give clues to the environment of their formation. Because they have a definite chemical formula, minerals tell us the chemical composition of the rock . For example, the composition of volcanic rocks can indicate whether the rocks formed in association with a mid-oceanic ridge, a subduction zone, or a hot spot. Figure 5. An example of a crystalline texture. Figure 6. An example of a porphyritic texture. Figure 3. An example of a clastic texture. Figure 4. An example of a foliated texture.
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Lab #2: Igneous Rocks 31 Lab #2: Igneous Rocks The purpose of today’s lab is to introduce you to igneous rocks. By the end of the lab you should be able to distinguish between different igneous rock types and interpret their origin. Objectives 1) Learn that every rock tells a story. 2) Know the difference between a rock and a mineral. 3) Know how to tell whether an igneous rock is felsic, intermediate, mafic, or ultramafic, and what the composition tells us about the tectonic setting of formation. 4) Igneous rock textures to know, and what they mean when you see them. 5) Recognize and describe the meaning of the following igneous rocks Plutonic: granite, diorite, gabbro, peridotite, dunite Volcanic: rhyolite, andesite, basalt 6) Conduct an experiment and explore how the density of igneous rocks controls plate tectonics. Materials Pencil (no pens) Textbook Calculator Pre-lab work (to be completed before lab begins) Complete the online Warm-Up Quiz using the information in this lab and your textbook, as well as the web links provided on the Canvas site. The ConcepTest will be on material related to plate tectonics from lab 1 and reading material from lab 2 (this lab). In-Class Activities (due by the end of lab today, requires a TA check) Activity 1: Igneous minerals Activity 2: Igneous rocks Activity 3: Density and plate tectonics Homework Activities (due the beginning of next lab) Activities on pages 42-44
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Lab #2: Igneous Rocks 32 Igneous Rocks Origin of Igneous Rocks Igneous rocks originate from molten rock. “Igneous” is derived from the Greek word for “fire” (think of ignite). Molten rock underground is called magma , and molten rock that erupts at the surface is called lava . Cooling of magma and lava produces igneous rocks. Magmas can flow easily or sluggishly, and this characteristic is described as their viscosity (resistence to flow). High viscosity (or viscous) magmas have high resistence to flow and flows slowly . Low viscosity magmas have low resistence to flow and flow easily. Viscosity is controlled by the magma’s chemical composition, fluid vs. mineral content, and temperature. For example, magma viscosity increases as it cools (the magma thickens). For more information about viscosity go to pg. 36.
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