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A magmatic rock with a phaneritic texture and medium-grained

A magmatic rock with a phaneritic texture and medium-grained

Applications and Investigations in Earth Science (9th Edition)
Applications and Investigations in Earth Science (9th Edition)
9th Edition
ISBN:9780134746241
Author:Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa
Publisher:Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa
Chapter1: The Study Of Minerals
Section: Chapter Questions
Problem 1LR
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Question 2 A magmatic rock with a phaneritic texture and medium-grained was petrographically examined under the microscope and the report is presented below: The rock contains anhedral to subhedral microcline crystals with variable grain sizes ranging between 1.5 mm and 3 mm. Most of the microcline display mild sericitization, and the estimated modal content is 20%. In some places there are subhedral crystals of perthitic orthoclase showing relatively coarse grains than microcline. The perthitic orthoclase constitute about 10% of the rock. The rock also contain subhedral to euhedral plagioclase lath-shaped crystals with a modal content of about 15%. Most of the plagioclase crystals display multiple twinning and display similar grain size to perthitic orthoclase. The anorthite content of plagioclase crystals was determined petrographically using the extinction angle technique and recorded anorthite content between 5% and 2%. Quartz grains display anhedral habits and variable grain sizes that range from 0.5 mm to 2.5 mm. In local places the quartz grains display wavey extinction particularly in places where they form aggregates. The modal content of quartz is estimated to be around 30%. The rock also contain biotite and hornblende as well as rare muscovite. Muscovite occurs sporadically within the sericitized microcline. Muscovite does not have a defined grain boundary. Within some biotite crystals there are relicts of chlorite with lilac colour. The modal contents of biotite and hornblende are 10% and 15%, respectively. The rock contains traces of apatite and zircon minerals. Based on the above petrographic description, answer the following questions: a) List the essential minerals in this rock. b) List the type minerals in this rock. c) List the secondary minerals in this rock. d) List the types of alterations in this rock. e) List the accessory minerals in this rock. f) Give the colour index and the name of the colour index of the rock. g) Classify the rock using the appropriate classification scheme. It should be clear how you arrived at the rock name. h) Give a fully qualified rock name.
Transcribed Image Text:Question 2 A magmatic rock with a phaneritic texture and medium-grained was petrographically examined under the microscope and the report is presented below: The rock contains anhedral to subhedral microcline crystals with variable grain sizes ranging between 1.5 mm and 3 mm. Most of the microcline display mild sericitization, and the estimated modal content is 20%. In some places there are subhedral crystals of perthitic orthoclase showing relatively coarse grains than microcline. The perthitic orthoclase constitute about 10% of the rock. The rock also contain subhedral to euhedral plagioclase lath-shaped crystals with a modal content of about 15%. Most of the plagioclase crystals display multiple twinning and display similar grain size to perthitic orthoclase. The anorthite content of plagioclase crystals was determined petrographically using the extinction angle technique and recorded anorthite content between 5% and 2%. Quartz grains display anhedral habits and variable grain sizes that range from 0.5 mm to 2.5 mm. In local places the quartz grains display wavey extinction particularly in places where they form aggregates. The modal content of quartz is estimated to be around 30%. The rock also contain biotite and hornblende as well as rare muscovite. Muscovite occurs sporadically within the sericitized microcline. Muscovite does not have a defined grain boundary. Within some biotite crystals there are relicts of chlorite with lilac colour. The modal contents of biotite and hornblende are 10% and 15%, respectively. The rock contains traces of apatite and zircon minerals. Based on the above petrographic description, answer the following questions: a) List the essential minerals in this rock. b) List the type minerals in this rock. c) List the secondary minerals in this rock. d) List the types of alterations in this rock. e) List the accessory minerals in this rock. f) Give the colour index and the name of the colour index of the rock. g) Classify the rock using the appropriate classification scheme. It should be clear how you arrived at the rock name. h) Give a fully qualified rock name.
Expert Solution
Step 1

a) Essential minerals in this rock are Quartz, K-feldspar (orthoclase and microcline), plagioclase, biotite and hornblende.

b) Types of minerals in this rock are microcline, orthoclase, plagioclase, anorthite, quartz, muscovite, biotite, hornblende with traces of apatite and zircon.

c) Secondary mineral in this rock is sericite.

d) Type of alteration in this rock is sericitization.

e) The accessory minerals in this rock are zircon, chlorite, muscovite, and apatite

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