lab 4 Geology

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342

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Geology

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Apr 3, 2024

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Ibrahim Marei Laboratory 4 Igneous Rocks CE 342 – Geology Dr. John Schuring – Spring 2024 1) Explain the difference between lava and magma. Amazingly heated fluid and semi-fluid stone known as magma is found beneath the surface of the Earth. It is known as lava when magma streams onto the surface of the Earth. 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? - Glassy igneous rocks (extrusive in nature) show the quickest cooling - The coarse the grain, the slower the cooling. Pegm. - Porphyritic suggests a shift in the 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 rock of each subgroup. - Igneous rocks with pale colors are found in felsic mineral groupings. (Quartz and feldspar are two examples.) - Igneous rocks with dark colors are found in mafic mineral groupings. (Biotite and pyroxene are two examples.) 4) Briefly describe magmatic differentiation and how it affects the mineral content of an igneous rock. A general phrase for the several processes by which magmas undergo mass compound change during the midway liquefying measure, cooling, emplacement, or emission is "magmatic differentiation." A magma series is a collection of magmas produced via volcanic separation.

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? The order of crystallization based on Bowen's Reaction Series for the minerals in pegmatite granite would be: 1- Quartz 2- Alkali-plagioclase (feldspar) 3- Muscovite Muscovite would likely display the best crystal form due to its platy structure and tendency to form well-defined crystals. 6) What is the most common rock in the oceanic crust that underlies the oceans? Basalts 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. Feldspar Feldspar Mica Quartz Quartz Mica

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 1 Pegmatite Phaneritic Light 30% Yes Yes No 2 Granite Phaneritic Light 35% Yes Yes No 3 Granodiorite Phaneritic Medium 30% Yes Yes No 4 Diorite Phaneritic Medium 50% Yes Yes No 5 Gabbro Phaneritic Dark 70% Yes No No 6 Anorthosite Phaneritic Medium 10% Yes No No 7 Basalt porphyry Porphyritic Dark 100% Yes Yes No 8 Monzonite Porphyritic Light 10% Yes Yes No 9 Rhyolite Aphanitic Micro Light 5% Yes Yes No 10 Andesite Aphanitic Micro Light 15% Yes No No 11 Tuff Aphanitic Micro Light 3% Yes No No 12 Obsidian Aphanitic Glassy Dark 100% No No No 13 Pitchstone Aphanitic Glassy Dark 100% No No No 14 Pumice Aphanitic Glassy Medium 80% No No No 15 Scoria Aphanitic Glassy Dark 90% No No No

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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): Specimen No. Luster Color Color Tone Igneous texture Visible Minerals Hardness Rock Name Int or Ext 1 Pearly White Light Phaneritic Feldspar H>4.5 Granite Int 2 Luster- glassy Black Dark Glassy None 2.5<H<4.5 Obsidian Ext 3 Dull Dark Brown Dark Aphanitic Feldspar H>4.5 Basalt Ext 4 Glassy Grey Medium Phaneritic Quartz/ feldspar H>4.5 Diorite Int 5 Dull White Light Aphanitic porous Feldspar H<2.5 Pumice Ext 6 Vitreous Orange Light Aphanitic None 2.5<H<4.5 Feldspar Ext 7 Vitreous Black Dark Pegmatitic Feldspar H>4.5 Pegmatitic gabbro Int 8 Dull Brown Dark Aphanitic porous None H<2.5 Scoria Ext 9 Dull Grey Dark Aphanitic porous None 2.5<H<4.5 Vesiclar basalt Ext 10 Vitreous White yellow Light Pegmatitic Quartz/ feldspar H>4.5 Pegmatitic Granite Int 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, In the front of the classroom, there is a special igneous structure known as columnar jointing. The rock type present in this specimen is basalt, a mafic extrusive igneous rock. Columnar jointing forms when basaltic lava cools and contracts, causing cracks to form in a hexagonal pattern as the lava solidifies. Columnar jointing is a fascinating igneous structure that forms in basaltic lava flows. The specimen in the classroom likely came from a volcanic eruption in the State of Maine, where basaltic lava flowed and cooled rapidly. As the lava cools, it contracts and forms cracks, which eventually develop into the distinctive hexagonal columns seen in the specimen.

lab 4 Geology

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