Optical Mineralogy

Fábio Braz Machado , Antonio José Ranalli Nardy

An essential work for anyone who is going to dwell on a petographic microscope!

Increasingly relevant, Optical Mineralogy is fundamental for good interpretation on the genesis of a rock, economic viability or even for geochemical data understanding.

The release of the book Optical Mineralogy, by Fábio Braz Machado and Antônio José R. Nardy, comes to fill an important void after decades without bibliography in Portuguese.

Didactic, the work uses clear language combined with several illustrations in order to facilitate minerals identification on the petrographic microscope.

The book addresses important characteristics, such as habits, cleavage, relief, partition, color, pleochroism and relation with crystallography, followed by the orthoscopic system with sign of elongation and types of extinction and conoscopic observation of minerals.

Original title
Mineralogia óptica
Year of publication

About the authors

Fábio Braz Machado

Fábio Braz Machado is a geologist (2003), master and PhD in Regional Geology (2004-2010) and postdoc (2012), all from São Paulo State University (Unesp). Author of the mineralogical online database of the Heinz Ebert Minerals and Rocks Museum (Unesp). He presided over the 46th Brazilian Geological Congress at Santos (SP) in the year of 2012. Since 2010 he is a professor in the Department of Exact and Earth Sciences at the Federal University of São Paulo and teaches Geochemistry, Environmental Geochemistry and Analytical Geochemistry. He has experience in the areas of Vulcanology, Mineralogy, Magmatic Petrology, and Geochemistry and Stratigraphy of the basalts of the Paraná Basin. Partner of the Sociedade Brasileira de Geologia since 2001.

Antonio José Ranalli Nardy

Antonio José Ranalli Nardy is a geologist from São Paulo State University (1981), master in Geophysics from University of São Paulo (1988) and PhD in Regional Geology from São Paulo State University (1996). Since 1985 he has been a professor in the Department of Petrology and Metallogeny of São Paulo State University and teaches Optical Mineralogy and Mineralogy. He has experience in the study of Petrology, Mineralogy and Geochemistry of volcanic rocks of the Serra Geral Formation, as well as in Analytical Geochemistry.

  1. Basic concepts


  1. The petrographic microscope and types of compounds for analysis
    • Generalities
    • Types of compounds for microscopic analysis
    • The petrographic or polarized light microscope
    • Objectives
    • Dry objectives and immersion
    • Oculars
    • The total visual increase of the microscope
    • Polarizer and analyzer
    • Platinum
    • Amici Bertrand lens
    • Capacitors
    • Iris diaphragm
    • Filters


  1. The indications of minerals
    • Isotropic minerals and uniaxial anisotropic
    • Uniaxial anisotropic minerals


  1. Observation of minerals under polarized natural light
    • Color
    • Relief
    • Determination of refractive indexes with immersion oils
    • Cleavage
    • Partition
    • Habit


  1. Observation of minerals under crossed nicols: orthoscopy
    • Principles of light interference
    • Interference colors
    • Effect of platinum rotation and extinction positions and maximum brightness
    • The compensators and positions of the slow and fast rays of a mineral
    • Determining the order of a certain color of interference
    • Birefringence
    • Determination of the thickness of a mineral grain
    • Angle and types of extinction
    • Elongation sign


  1. Conoscopic examination of minerals
    • The interference figures of the uniaxial minerals
    • The interference figures of biaxial minerals


Annex A1

Colorful figures

Bibliographical references

Presentation and preface

It is a great pleasure for me to have the privilege of presenting the work Optical Mineralogy, written by competent geologists, academicians, colleagues and friends Fábio Braz Machado and Antonio José Ranalli Nardy. Written in clear and objective style, this book will surely be of great value to researchers and students of this important branch of Mineralogy that deals with the characterization of minerals under the petrographic microscope.
Both authors are longstanding specialists in mineralogy and petrology of volcanic rocks in general, and their particular scientific concern has been the study of the Magmatic Province of Paraná, which is of great importance for its geographical extension in the South of Brazil, because of their great interest in the geological history of South America.
The first author, Fábio Braz Machado, graduated in Geology from Unesp in 2003, obtained his Master’s and PhD degree from the same university and is currently a professor at Unifesp. Worthy of recognition is his performance at the Brazilian Society of Geology, where he was president of the São Paulo nucleus and also president of the 46th Brazilian Congress of Geology in 2012. He is currently the secretary-general of the Brazilian Society of Geology. The second author, Antonio José Ranalli Nardy, also graduated in Geology from Unesp in 1981, obtained his Master’s degree in Geophysics from IAG-USP (Institute of Astronomy, Geophysics and Atmospheric Sciences – USP) and his PhD in Regional Geology from Unesp. Nardy is also a researcher at the CNPq, and was Fabio’s research director in both the Master’s and PhD programs. They both teach in the area of Petrology and Geochemistry of Igneous Rocks and share responsibility for the specific discipline of Optical Mineralogy for several years.
When it comes to the contents of this book, its introductory chapter is a synthetic critical revision of the basic theoretical concepts of Optical Physics, and the second chapter shows how the petrographic microscope works and also what happens when polarized lights affects the mineral to be studied. The next four chapters, the most important ones of the book, are of an eminently practical nature, with the purpose of making the optical crystallography of minerals understandable and how their optical characteristics can be determined under the microscope. The importance of this work is a result of the fact that there are practically no didactic books that can satisfy with the necessary depth the present subject, in an area like the one of Mineralogy, in which the very existing books are very few. The book by Fábio and Nardy has its text directed to the students and professionals of the workstream and illustrations carefully adapted for what they intend to demonstrate.
In my opinion, there is no doubt that Optical Mineralogy is indispensable for all researches of Geology and Petrology who work with identification of minerals in rocks and especially for the students of this discipline, usually mandatory in the 36 courses of Geology and Geological Engineering that exist in Brazil.

Umberto G. Cordani
August 2016

Few are the national books that deal with this important subject that is the identification of minerals under the petrographic microscope. The only exclusive work on the subject was published almost 40 years ago. Unfortunately, until now, the publications are restricted to international works in foreign language and not translated to Portuguese.
Optical Mineralogy, or the study of minerals under the microscope, is a mandatory discipline in the courses of Geology and Geological Engineering, essential for the understanding of Petrology, Crystallography, Prospecting, Economic Geology, Paleontology and Pedology. It is about the pillar of a good interpretation on the genesis of a rock, economic viability or even the understanding of a geochemical data.
In a way, over the years, with the technological modernization of petrographic microscopes, especially in the treatment of images, and the emergence of new manufacturers in the market, the cost has been cheaper. This promoted its dissemination in the geology and mining companies, increasing the level of demand of knowledge about Mineralogy and Petrography of the professional in comparison to what was demanded until then.
Textures, structures, porosity became common terms in the daily life of professionals in the field of mining or prospecting. Thus, “crossing the nichols” became a common phrase for the geologist. Therefore, this book fills a gap in national geoscientific knowledge. Written in an easy, pleasant, dynamic way and with many carefully drawn figures, it takes the reader to answer about the most diverse tools of identification of minerals under the microscope.
The book begins with the basic properties of Optical Physics, leading the reader to understand the behavior of light incident on the mineral. After this, important characteristics such as habit, cleavage, relief, partition, color, pleochroism and relation with crystallography are discusses, following the orthoscopic system with sign of elongation and types of extinction.
At the end, conoscopy is discussed, with types of interference figures for uniaxial and biaxial minerals (some of them absent in the international literature) and measurement and formation of the 2V angle.
Finally, the authors wish immensely that this book to be a useful tool, important for students and professionals who need to know, or remember, techniques of using the petrographic microscope.

The authors