Lab 5 Assignment F23
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University of Waterloo *
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MISC
Subject
Geology
Date
Apr 3, 2024
Type
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9
Uploaded by DoctorBear1290
LAB 5: IGNEOUS ROCKS 1. INTRODUCTION Complete the following questions during the lab, and submit it to the dropbox 24hrs after the lab is done. You should be able to complete 98%
of the work in the lab, however, you will need to add some photos to your document/assignment. Use the following as a guide to know what level of detail we are looking for when you complete the information for this lab and future labs. Also take a look at the examples on the next page. Sample # Texture, grain size, shapes, etc Mineralogy and/or colour Rock Name Textures: Aphanitic or phaneritic are a must, plus any other important textural terms (vesicular, porphyritic, etc) Grain size: For a phaneritic rock, include grain size –
use the terms fine, medium and coarse grained as defined in your lab manual. If the rock is porphyritic, list the grain sizes of both parts of the rock –
the phenocryst and groundmass (or matrix). Use n/a for aphanitic and other textures with no visible grain sizes Grain Shapes (and/or any additional descriptive terms):
Are identifiable grains euhedral? What are the crystal shapes? Subhedral? Anhedral? What are the shapes? For a aphanitic rock –
describe it’s colour
For a phaneritic rock –
List % composition of minerals. Start by stating the the amount of felsic vs. mafic minerals. This is an important first step!!! From there, subdivide further. Where you can, determine the %o of felsic minerals present –
subdivide between quartz, muscovite and feldspar. Where you can, subdivide the Plagioclase vs. alkali feldspars Where you can, sub divide the % mafic minerals in term of olivine/pyroxenes/amphibole/biotite. Porphyritic –
describe the mineralogy of both parts of the rock –
the smaller and the larger grained component (usually the groundmass and the phenocrysts) For porphyritic rocks –
. Determine the % phenocrysts and % groundmass then follow the steps for phaneritic or aphanitic rocks for EACH of these components, depending on their texture Use the rock ID chart you are given to identify the type of rock. Modify the rock name with any important textural and/or mineralogical terms if need be.
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3 2. PART 1 - FELSIC AND INTERMEDIATE IGNEOUS ROCKS Rock # Texture, grain size, shapes, etc Mineralogy or colour (depending on texture) Rock Name 9 Textures: Phaneritic Grain Size: Medium Grain Grain Shapes (and/or any additional descriptive terms): Subconchoidal shape Euhedral <10% MAFIC - 100% BIOTITE 90% FELSIC - 45% Quartz - 45% Na rich Plagioclase Feldspar Rock Name (from ID chart): Granite Photo (with scale!) 10 Textures: Phaneritic and porphyritic Grain Size: Course Grain Grain Shapes (and/or any additional descriptive terms: Differing shapes, some circular, some rectangular Anhedral Hint
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there are two parts to this rock, make sure to describe the mineralogies separately 60% Bigger chunks (Matrix) - 60% Potassium Feldspar 40% Smaller chunks (Phenocryst) -15% Mafic - 10% Biotite - 5% Amphibole - 85% Felsic (45% Potassium Feldspar and 40% Quartz) Rock Name (from ID chart): Granite Photo (with scale!) 11 Textures: Phaneritic Hint –
is there any quartz in this rock? Most of what you are seeing in this rock are light grey feldspars. Can you Rock Name (from ID chart): Diorite
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4 Rock # Texture, grain size, shapes, etc Mineralogy or colour (depending on texture) Rock Name Grain Size: Fine to Medium Grain Grain Shapes (and/or any additional descriptive terms: Subconchoidal shapes Euhedral determine which one? There is also~10% biotite in this sample 90% Felsic (90% Plagioclase feldspar) 10% Mafic (10% Biotite) Photo (with scale!) 12b Textures: Phaneritic Grain Size: Fine to Medium Grain Grain Shapes (and/or any additional descriptive terms: Anhedral More rectangular is Mafic 60% Felsic (5% Quartz, 50% Plagioclase feldspar, 5% potassium feldspar) 40% Mafic (5% Biotite, 17.5% Pyroxene, 17.5% Amphibole) Hard to distinguish pyroxene and amphibole Rock Name (from ID chart): Diorite Photo (with scale!) 13 Textures: Aphanitic <5% Mafic (5% Biotite) Rock Name (from ID chart): Rhyolite
5 Rock # Texture, grain size, shapes, etc Mineralogy or colour (depending on texture) Rock Name Grain Size: Too find to tell Grain Shapes (and/or any additional descriptive terms: Too hard to tell >95% Felsic (90% Potassium feldspar, 5% Quartz) Photo (with scale!) 14 Textures: Phenocryst= Aphanitic Matrix= Phaneritic Grain Size: Matrix are medium Grain Shapes (and/or any additional descriptive terms: Rectangular Euhedral Hint
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there are two parts to this rock, make sure to describe the mineralogies separately 95% matrix Aphanitic 70% Mafic (40% Amphibole, 30% Pyroxene) 30% Felsic (30%Plagioclase feldspar) 5% phaneritic phenocryst
5% mafic (5% Amphibole) Rock Name (from ID chart): Andesite Photo (with scale!) 15 Textures: Porphyritic and phaneritic Grain Size: Phenocryst is Course Matrix is fine Grain Shapes (and/or any additional descriptive terms: Phenocryst are big and rectangular Matrix are too small to tell Hint
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there are two parts to this rock, make sure to describe the mineralogies separately 60% Matrix 100% Mafic (80% amphibole, 20% Biotite) 40% Phenocryst 100% Felsic (80% Plagioclase feldspar, 20% Potassium feldspar) Rock Name (from ID chart): Trachyte Photo (with scale!)
6 Rock # Texture, grain size, shapes, etc Mineralogy or colour (depending on texture) Rock Name 16a & b Textures: Glassy Grain Size: Too fine to tell Grain Shapes (and/or any additional descriptive terms: N/A From chart 80% Felsic (20% Quartz, 40% Potassium feldspar, 20% Plagioclase feldspar) 20% Mafic 14% Amphibole 6% Biotite Rock Name (from ID chart): Obsidian Photo (with scale!) 17 Textures: Aphanitic Grain Size: Too fine to tell Grain Shapes (and/or any additional descriptive terms: Too fine to tell 100% Felsic (92% Potassium feldspar, 8% Quartz) Rock Name (from ID chart): Pumice Photo (with scale!)
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7 3. PART 2 - MAFIC AND ULTRAMAFIC IGNEOUS ROCKS Rock # Texture, grain size, shapes, etc Mineralogy or colour (depending on texture) Rock Name 1 Textures: Phaneritic Grain Size: Fine Grained Grain Shapes (and/or any additional descriptive terms: Some Rectangular but not all are and are very inconsistent Subhedral Ultramafic with >90% olivine and pyroxene. May have minor amounts of plagioclase, hornblende or mica. Difficult to identify. Rock Name (from ID chart): Peridotite Photo (with scale!) 2 Textures: Phaneritic Grain Size: Medium Grain Grain Shapes (and/or any additional descriptive terms: Rectangular shaped Euhedral %50 feldspars –
can you determine which one? What is your evidence? Calcium rich Feldspar. This is because the chart has the evenly distributed felsic and mafic minerals being mostly calcium rich feldspar 50% mafic minerals –
most likely pyroxene Rock Name (from ID chart): Diabase Photo (with scale!) 3 Textures: Phaneritic Grain Size: Fine to medium grained Grain Shapes (and/or any additional descriptive terms: Euhedral as well as being rectangular 40% Plagioclase (dark grey) 50% Pyroxene (black) 10% silvery Sulphides (Ni ore!) 35% Felsic 65% Mafic Rock Name (from ID chart): Norite (a 2 pyroxene gabbro) Photo (with scale!)
8 Rock # Texture, grain size, shapes, etc Mineralogy or colour (depending on texture) Rock Name 4a Textures: Aphanitic Grain Size: Too Fine grain size to tell Grain Shapes (and/or any additional descriptive terms): Too fine to tell >95% Mafic (Over 75% pyroxene) <5% Felsic (5% Plagioclase feldspar) We got these percentages from the chart Rock Name (from ID chart): Basalt Photo (with scale!) 5 Textures: Porphyritic Phaneritic Grain Size: Fine Grain Grain Shapes (and/or any additional descriptive terms: Shapes are irregular that are within the rock. Anhedral Hint
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there are two parts to this rock, make sure to describe the mineralogies separately 80% Matrix >95% Mafic (Over 75% pyroxene) <5% felsic 5% Plagioclase feldspar 20% Phenocryst >15% Green Olivine <5% Calcium rich Plagioclase feldspar Got these percentages from the chart Rock Name (from ID chart): Gabbro Photo (with scale!) 6 Textures: Vesicular Dark grey Rock Name (from ID chart): Scoria
9 Rock # Texture, grain size, shapes, etc Mineralogy or colour (depending on texture) Rock Name Grain Size: Aphanitic Grain Shapes (and/or any additional descriptive terms: None since Aphanitic Photo (with scale!) 7 Textures: Make sure to use the correct textural term to describe the white mineral
Vesicular Grain Size: Very fine grained Grain Shapes (and/or any additional descriptive terms: Subhedral 60% Mafic (40% Olivine, and 20% Pyroxene) Got these percentages from the chart 40% Felsic (All 40% Ca rich Plagioclase feldspar) I wrote amygdule and I know that amygdule is Calcite Rock Name (from ID chart): Amygdule Basalt Photo (with scale!) 8 Textures: Vesicular Grain Size: Aphanitic Grain Shapes (and/or any additional descriptive terms: None since Aphanitic Very dark grey. Also has some reddish tones going through it. Rock Name (from ID chart): Scoria Photo (with scale!)
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