This sample is a felsic igneous rock. You can tell it is a volcanic rock because of the presenceof glass and the porphyritic texture. The glass in this rock forms the matrix around the mineralsand is isotropic. This rock contains plagioclase feldspar, quartz, sanidine, and a common maficphase. Sanidine is an alkali feldspar which typically forms euhedral, blocky crystals with twocleavage planes and low interference colors (similar to plagioclase). It also has distinctiveCarlsbad twinning (simple twins that divide a grain into two domains) **Question B:** How would you distinguish quartz from alkali feldspar in thin section? Please list at least two properties for each mineral type that can be used to differentiate quartz and potassium feldspar.In a thin section analysis, quartz and alkali feldspar can be distinguished based on several optical and physical properties. Here are two properties that can help differentiate each mineral type:**Quartz:**1. **Lack of Cleavage:** Quartz does not exhibit cleavage, meaning it does not break along defined planes. This can be observed under the microscope as an absence of consistent fracture lines.2. **Undulatory Extinction:** Quartz often shows undulatory extinction, which appears as a wavy pattern under polarized light.**Potassium Feldspar:**1. **Cleavage Lines:** Potassium feldspar shows good cleavage, typically in two directions at nearly 90 degrees. This can be identified as distinct lines or fractures under the microscope.2. **Twinning:** Potassium feldspar often exhibits twinning, particularly Carlsbad twinning, which is visible as repeated patterns in polarized light.

Igneous rocks are rock types that originate from the solidification of molten material, which can be…

Answered: B. How would you distinguish quartz…

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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This sample is a felsic igneous rock. You can tell it is a volcanic rock because of the presence
of glass and the porphyritic texture. The glass in this rock forms the matrix around the minerals
and is isotropic. This rock contains plagioclase feldspar, quartz, sanidine, and a common mafic
phase. Sanidine is an alkali feldspar which typically forms euhedral, blocky crystals with two
cleavage planes and low interference colors (similar to plagioclase). It also has distinctive
Carlsbad twinning (simple twins that divide a grain into two domains)