Lab 4 - Igneous Rev2 - F23

Laboratory 4 – Rev2 Igneous Rocks CE 342 – Geology Dr. John Schuring – Fall 2023 1) Explain the difference between lava and magma. 2) The texture of an igneous rock is largely determined by the rate of cooling. Which texture indicates the fastest cooling? The slowest? Which texture indicates there was a change in rate? 3) The color tone of an igneous rock is an indicator of its chemical composition. Light colored igneous rocks have an abundance of which mineral subgroup? How about dark colored igneous rocks? Give two example minerals of each subgroup. 4) Briefly describe magmatic differentiation and how it affects the mineral content of an igneous rock. 5) You spot the following minerals in a hand specimen of pegmatite granite: quartz, alkali- plagioclase, and muscovite. Using Bowen ’ s Reaction Series, determine the order of crystallization, i.e., which formed first, second, etc.? Also, which of the three minerals would likely display the best crystal form? 6) What is the most common rock in the oceanic crust that underlies the oceans? 7) Granite Close-up: Examine the Granite Closeup photo posted on Canvas. Transfer it to your homework sheet and identify the three basic minerals: feldspar, quartz and mica. Use leader arrows and labels to make the identifications. Identify each mineral at two different locations on the photo, i.e., two leader lines to quartz at various points, etc. 8) 15 Specimen Collection: Examine and study the identified igneous rock collection provided. Compare the specimens with the information in the Class Notes and AGI Data Sheet 23.1 (next page). Fill in the information in the table below. Specimen No. Rock Name Igneous Texture Color Tone % Dark Minerals Feldspar Visible? Quartz Visible? Other Features? 9A) Unidentified Specimens: Using your available references (Table 3.1.1, Figure 3.1.19, Class Notes), identify the 10 unknown specimens displayed at the front of the classroom. Describe each specimen thoroughly with regard to color, color tone, texture, and visible minerals. Present your findings in the following format (landscape): IGNEOUS ROCK ANALYSIS SUMMARY Specimen No. Luster Color Color Tone Igneous Texture Name any individual minerals that you can see? Hardness Name the Rock! Intrusive or Extrusive 9B) Special Igneous Structure Examine the special specimens in the front of the classroom. Take a photo of it and insert in your lab report. Then do the following: (1) Name the igneous structure/feature (2) Identify the rock types; and (3) Write 1-2 sentences about how the specimen was formed. Note that this was collected from the State of Maine,