Discover the Beauty and Diversity of Minerals in Thin Section with Dexter Perkins' Second Edition
Minerals in Thin Section (2nd Edition) Dexter Perkins
If you are interested in learning more about minerals and how they look under a microscope, you might want to check out the book Minerals in Thin Section (2nd Edition) by Dexter Perkins. This book is a comprehensive and accessible introduction to optical mineralogy, which is the study of minerals using polarized light. In this article, I'll give you an overview of what a thin section is, why it is useful for studying minerals, what are some of the optical properties and common minerals you can observe in thin sections, and how you can use this book effectively to enhance your knowledge and skills in optical mineralogy.
Minerals in Thin Section (2nd Edition) Dexter Perkins
What is a thin section?
A thin section is a very thin slice of rock or mineral that is mounted on a glass slide and viewed under a microscope with polarized light. A typical thin section is about 0.03 mm thick, which is thin enough to allow light to pass through it. To prepare a thin section, a rock or mineral sample is first cut into a small piece, then ground and polished on both sides until it reaches the desired thickness. The sample is then glued to a glass slide and covered with a cover slip to protect it from dust and scratches.
Thin sections are used in mineralogy because they reveal the internal structure and composition of minerals that are not visible to the naked eye or with a hand lens. By using polarized light, you can observe how different minerals interact with light and display various colors, patterns, and optical effects. These optical properties can help you identify, classify, and characterize minerals based on their crystal structure, chemical composition, and physical properties.
Why study minerals in thin section?
Studying minerals in thin section has many benefits and applications for various fields and disciplines. Some of the reasons why you might want to study minerals in thin section are:
To learn about the diversity and beauty of minerals and rocks in nature.
To understand the formation and evolution of minerals and rocks in different geological environments and processes.
To determine the mineral composition and texture of rocks and how they relate to their origin and history.
To identify unknown minerals and rocks based on their optical properties and characteristics.
To classify and name minerals and rocks according to established systems and standards.
To characterize and quantify the physical, chemical, and mechanical properties of minerals and rocks for various purposes.
To explore the relationship between minerals and rocks and other natural phenomena, such as climate, biology, magnetism, etc.
To apply the knowledge and skills of optical mineralogy to other disciplines, such as geology, petrology, geochemistry, geophysics, engineering, etc.
Optical properties of minerals
Before you start looking at minerals in thin section, you need to familiarize yourself with some basic concepts and terminology of optical mineralogy. Optical mineralogy is the branch of science that deals with the interaction of light and minerals and how it affects their appearance and behavior under a microscope. Some of the optical properties of minerals that you can observe in thin sections are:
Refractive index: The ratio of the speed of light in a vacuum to the speed of light in a mineral. It measures how much a mineral bends or refracts light as it passes through it. Different minerals have different refractive indices depending on their crystal structure and chemical composition. The refractive index can be measured using a refractometer or calculated from other optical properties.
Birefringence: The difference between the maximum and minimum refractive indices of a mineral. It measures how much a mineral splits or polarizes light into two rays as it passes through it. Birefringence is a property of anisotropic minerals, which are minerals that have different optical properties in different directions. The birefringence can be observed as interference colors or color changes when rotating a thin section under crossed polarizers.
Interference colors: The colors produced by the interference of two polarized light rays that pass through a birefringent mineral. The interference colors depend on the thickness of the thin section, the wavelength of light, and the birefringence of the mineral. The interference colors can be used to estimate the birefringence or thickness of a mineral using a Michel-Lévy chart or an interference color chart.
Extinction angle: The angle between a crystallographic axis or cleavage direction of a mineral and the direction of extinction or darkness under crossed polarizers. It measures how much a mineral rotates or changes its polarization plane as it passes through it. The extinction angle can be used to identify or distinguish minerals based on their symmetry or crystal system.
Common minerals in thin section
There are thousands of different minerals in nature, but only a few dozen are commonly found in thin sections. These common minerals are usually classified into major groups based on their chemical composition or structure, such as silicates, carbonates, oxides, sulfides, etc. Some of the most common minerals that you can encounter in thin sections are:
Quartz: A silicate mineral that is composed of silicon and oxygen (SiO2). It is one of the most abundant and widespread minerals on Earth. It has a hexagonal crystal system and no cleavage. It is colorless or white in thin section, with low relief and low birefringence. It has straight extinction or undulose extinction due to deformation.
Feldspar is a group of silicate minerals that are composed of various combinations of aluminum, silicon, oxygen, and alkali metals or alkaline earth metals (e.g., KAlSi3O8, NaAlSi3O8, CaAl2Si2O8). They are the most abundant group of minerals in the Earth's crust. They have a triclinic or monoclinic crystal system and two or three directions of cleavage. They are usually white, gray, pink, or green in thin section, with low to moderate relief and low to high birefringence. They often show twinning or zoning patterns due to different compositions or growth stages.
Mica is a group of silicate minerals that are composed of layers of tetrahedra and octahedra that are held together by weak bonds (e.g., KAl2(AlSi3O10)(OH)2, K(Mg,Fe)3(AlSi3O10)(OH)2). They are common in metamorphic and igneous rocks. They have a monoclinic crystal system and one perfect direction of cleavage. They are usually colorless, brown, green, or purple in thin section, with low relief and moderate to high birefringence. They often show pleochroism or color changes due to different orientations of the crystal.
Amphibole is a group of silicate minerals that are composed of double chains of tetrahedra and various cations (e.g., Ca2(Mg,Fe)5Si8O22(OH)2, NaCa2(Mg,Fe)5Si8O22(OH)2). They are common in metamorphic and igneous rocks. They have a monoclinic crystal system and two directions of cleavage at 56 and 124. They are usually colorless, green, brown, or black in thin section, with moderate to high relief and moderate to high birefringence. They often show extinction angles or oblique angles between the cleavage directions and the extinction direction.
Pyroxene is a group of silicate minerals that are composed of single chains of tetrahedra and various cations (e.g., CaMgSi2O6, MgFeSi2O6, NaAlSi2O6). They are common in igneous and metamorphic rocks. They have an orthorhombic or monoclinic crystal system and two directions of cleavage at 87 and 93. They are usually colorless, green, brown, or black in thin section, with moderate to high relief and low to high birefringence. They often show extinction angles or parallel angles between the cleavage directions and the extinction direction.
Olivine is a silicate mineral that is composed of isolated tetrahedra and magnesium and iron cations (e.g., (Mg,Fe)SiO). It is common in mafic and ultramafic igneous rocks. It has an orthorhombic crystal system and no cleavage. It is usually colorless or yellow-green in thin section, with high relief and low birefringence. It often shows fractures or cracks due to its brittleness.
Special techniques and topics in thin section analysis
Besides the basic optical properties and common minerals that you can observe in thin sections, there are also some advanced or specialized methods and topics that you can explore in optical mineralogy. Some of these techniques and topics are:
Interference figures: The patterns or shapes produced by the interference of polarized light rays that pass through a mineral under convergent light. They can be observed by using a Bertrand lens or a conoscopic lens that focuses the light rays to a point. Interference figures can reveal the symmetry, optical character, and optic sign of a mineral.
Dispersion staining: A technique that uses the dispersion or variation of refractive index with wavelength of light to produce color differences between minerals or phases. It can be performed by using a special objective lens that has a small aperture and a colored filter. Dispersion staining can help identify minerals or phases that have similar optical properties but different dispersion values.
Fluid inclusions: Tiny cavities or bubbles that contain fluids (e.g., water, gas, oil, etc.) that were trapped in a mineral during its formation or growth. They can be observed by using a heating or cooling stage that changes the temperature and pressure of the thin section. Fluid inclusions can provide information about the origin, environment, and evolution of minerals and rocks.
Metamorphic textures: The arrangement or distribution of minerals or grains in a metamorphic rock that reflects the conditions and processes of metamorphism. They can be observed by using a polarizing microscope or a scanning electron microscope. Metamorphic textures can include foliation, banding, porphyroblasts, etc.
How to use the book Minerals in Thin Section (2nd Edition) Dexter Perkins
Now that you have some background knowledge on what a thin section is and why it is important for studying minerals, you might be wondering how to use the book Minerals in Thin Section (2nd Edition) by Dexter Perkins effectively for learning and teaching optical mineralogy. This book is designed to be a practical and user-friendly guide that covers the essential concepts and skills of optical mineralogy and provides numerous examples and exercises to help you apply them to real thin sections. Here are some tips on how to use this book efficiently:
The structure and content of the book
The book is divided into 12 chapters and 4 appendices that cover the following topics:
Chapter 1: Introduction: This chapter introduces the basic principles and equipment of optical mineralogy, such as light, polarization, microscope, thin section, etc.
Chapter 2: Isotropic Minerals: This chapter explains the optical properties and identification of isotropic minerals, which are minerals that have the same optical properties in all directions.
Chapter 3: Uniaxial Minerals: This chapter explains the optical properties and identification of uniaxial minerals, which are anisotropic minerals that have one optic axis or direction of symmetry.
Chapter 4: Biaxial Minerals: This chapter explains the optical properties and identification of biaxial minerals, which are anisotropic minerals that have two optic axes or directions of symmetry.
Chapter 5: Optic Orientation: This chapter explains how to determine the orientation of crystals or grains in thin sections based on their optical properties and interference figures.
Chapter 6: Optical Mineralogy of Common Rock-Forming Minerals: This chapter summarizes the physical and optical characteristics of the most common rock-forming minerals in thin sections, such as quartz, feldspar, mica, amphibole, pyroxene, olivine, etc.
Chapter 7: Optical Mineralogy of Less Common Rock-Forming Minerals: This chapter summarizes the physical and optical characteristics of some less common rock-forming minerals in thin sections, such as garnet, epidote, calcite, dolomite, etc.
Chapter 8: Optical Mineralogy of Opaque Minerals: This chapter summarizes the physical and optical characteristics of opaque minerals in thin sections, such as magnetite, hematite, pyrite, etc.
Chapter 9: Optical Mineralogy of Non-Silicate Minerals: This chapter summarizes the physical and optical characteristics of some non-silicate minerals in thin sections, such as carbonates, sulfates, phosphates, etc.
Chapter 10: Special Topics: This chapter covers some special topics and techniques in optical mineralogy, such as dispersion staining, fluid inclusions, metamorphic textures, etc.
review exercises and questions to test your knowledge and skills in optical mineralogy.
Chapter 12: Answers to Review Exercises: This chapter provides the answers and explanations to the review exercises and questions in Chapter 11.
Appendix A: Mineral Tables: This appendix provides some tables that list the physical and optical properties of common minerals in thin sections.
Appendix B: Interference Color Chart: This appendix provides a chart that shows the interference colors of minerals in thin sections based on their birefringence and thickness.
Appendix C: Michel-Lévy Chart: This appendix provides a chart that shows the interference colors of minerals in thin sections based on their birefringence and retardation.
Appendix D: Glossary: This appendix provides a glossary of terms and definitions used in optical mineralogy.
The book is organized in a logical and progressive way that allows you to learn the concepts and skills of optical mineralogy step by step. Each chapter starts with a list of learning objectives and ends with a summary of key points. The book also uses many figures, diagrams, tables, and photographs to illustrate and explain the topics. The book also includes many examples and exercises that help you practice and apply what you have learned to real thin sections. The book also provides some tips and tricks to help you avoid common mistakes and difficulties in optical mineralogy.
The accompanying CD-ROM and website
In addition to the book content, you also have access to some additional resources that supplement and enhance your learning and teaching experience. These resources are provided by the accompanying CD-ROM and website that come with the book. Some of these resources are:
Interactive tutorials: These are interactive modules that guide you through the concepts and skills of optical mineralogy using animations, simulations, quizzes, etc. They are designed to help you visualize and understand the topics better.
Virtual microscope: This is a software program that allows you to view and manipulate thin sections on your computer screen using a virtual microscope. You can adjust the magnification, focus, illumination, polarization, rotation, etc. You can also measure the optical properties of minerals using tools such as refractometer, Bertrand lens, conoscopic lens, etc. You can also compare different thin sections or minerals using a split screen or overlay mode.
Thin section gallery: This is a collection of high-quality images of thin sections that show various minerals, rocks, textures, etc. You can browse, search, zoom, rotate, etc. the images. You can also view the images under different lighting conditions or polarization modes. You can also access some information or data about each image.
Additional exercises and questions: These are some additional exercises and questions that help you practice and test your knowledge and skills in optical mineralogy. They are similar to the ones in the book but cover different topics or levels of difficulty. You can also access the answers and explanations to these exercises and questions.
The CD-ROM and website resources are designed to complement and support the book content. They provide you with more opportunities to learn, practice, and apply optical mineralogy in an interactive and engaging way. They also provide you with more feedback and guidance to help you improve your performance and confidence in optical mineralogy.
In this article, I have given you an overview of what a thin section is, why it is useful for studying minerals, what are some of the optical properties and common minerals you can observe in thin sections, and how you can use the book Minerals in Thin Section (2nd Edition) by Dexter Perkins effectively for learning and teaching optical mineralogy. I hope this article has sparked your interest and curiosity in optical mineralogy and encouraged you to explore this fascinating and rewarding field further. Optical mineralogy is not only a valuable skill for geologists, but also a fun and enjoyable hobby for anyone who loves nature and appreciates its beauty and diversity.
Here are some frequently asked questions and answers related to the topic of this article:
Q: How can I get access to a polarizing microscope and thin sections?
A: You can get access to a polarizing microscope and thin sections by enrolling in a geology course or joining a geology club at your school or local community. You can also buy or rent a polarizing microscope and thin sections from online or offline suppliers or dealers. You can also make your own thin sections by following some instructions and tutorials available online or in books.
Q: How can I learn more about optical mineralogy and related topics?
A: You can learn more about optical mineralogy and related topics by reading books, articles, journals, or websites on the subject. You can also watch videos, podcasts, webinars, or lectures on the subject. You can also take online or offline courses, workshops, or seminars on the subject. You can also consult experts, instructors, or mentors on the subject.
Q: How can I improve my skills and performance in optical mineralogy?
A: You can improve your skills and performance in optical mineralogy by practicing regularly and frequently using thin sections and a polarizing microscope. You can also review and reinforce your knowledge and understanding of the concepts and principles of optical mineralogy. You can also challenge yourself by trying different or difficult thin sections or minerals. You can also seek feedback an