00799 - Petrography

Course Unit Page


This teaching activity contributes to the achievement of the Sustainable Development Goals of the UN 2030 Agenda.

Quality education Sustainable cities

Academic Year 2021/2022

Learning outcomes

Students will learn the basic tools to describe and classify igneous and metamorphic rocks, and understand the petrogenetic processes and their geologic significance. Students will acquire the know-how to classify in the field (= outcrop scale) and in the lab (hand sample) igneous and metamorphic rocks.

Course contents

Igneous rocks - The magma: physical and chemical features. Upwelling and solidification of magmas: intrusive vs. volcanic settings. Origin of mantle magmas. Igneous differentiation: fractional crystallization, gravitative setting and cumulus rocks, assimilation, mixing and mingling of different melts. Bowen's reaction series. Anatectic magmas and origin of granites. Mineralogical and chemical features of igneous rocks. Classification of igneous rocks. Magmatic series and their relation to different geodynamic settings.

Metamorphic rocks - Definition and its drivers: pressure, temperature, deformation and fluids. Meso/microstructures and their classification. How to classify a metamorphic rock. Netamorphic reactions and the record they left into the rocks. Metamorphic grade and facies. Metamorphic facies series. Geotherm and Pressure-Temperature-time paths. Regional metamorphism (subduction, orogenic and sea floor) and contact metamorphism. Analysis and interpretation of mineral assemblages in metabasites and metapelites.

Lab activities - Classification of hand-sized samples of igneous, and metamorphic rocks.  

Field Trip - A single-day excursion with practical exercises of classification of igneous and metamorphic rocks


Klein C., Philpotts A. (2018) Mineralogia e Petrografia (1a ed. italiana), Bologna, Zanichelli. Pagine: 544. ISBN: 978880832060

which is the Italian translation of

Klein, C., & Philpotts, A. (2012). Earth Materials: Introduction to Mineralogy and Petrology. Cambridge: Cambridge University Press. doi:10.1017/CBO9781139028028


Teaching methods

Class lectures augmented by

  • Home work
  • Petrography Lab
  • Field Excursion

The teaching methods of this course require that all students must attend the Module 1 and 2 of the Online courses on Health and Safety in Study and Research Areas - Module 1 and 2, while the Module 3 on health and safety is to be attended in class.

Information about Module 3 attendance and schedule is available on the website of your degree programme.

Assessment methods

(the information below may change according to the SARS-COV-2 pandemic evolution)

The assessment of the learning goals consists of an oral exam in which we will test

  1. skills in the recognition of minerals and structures and classification of rocks and
  2. knowledge of the main topics covered in class.

As for point (1), the student must be able to:

  • know and understand the basic terms (= basic knowledge) to describe a rock at the different observation scales,
  • apply basic knowledge to the proposed images,
  • logically organize the information the student will be able to obtain from the analysis of the rock samples,
  • critically evaluate what has been observed, highlighting the limits of observation and how one could overcome these limits.

A practical example:

I observe an image of a phaneritic rock with a low color index (<40) and in which I certainly recognize quartz. The structure is hypidiomorphic granular. It could be a tonalite, a granodiorite, a monzogranite, a sienogranite or an alkali-feldspar granite.

The correct classification is based on the evaluation of the alkalifeldspar / plagioclase modal ratio and, secondly, on the type of femic minerals.

The possible answers are (listed in order of increasing critical approach, which is proportional to the vote ...)

1. it is a granitoid,

2. it can be a tonalite or a granodiorite (or, for example, a granite or a granodiorite, or a sienogranite or an alkalifeldspar granite)

3. it can be a tonalite or a granodiorite (or one of the other two pairs of lithotypes of the previous point); to improve the classification, I would try to estimate the orthoclase vs plagioclase modal abundances. To do this, I would observe on the hand sample how many minerals reflect light on their cleavage planes (orthoclase) compared to those that do not have this property because they have a less developed cleavage (plagioclase). Also, I would try to better understand the type of femic mineral because tonalites often have amphibole while granites are more likely to have biotite as the main femic.

All the answers are correct but the answer (3) shows a greater petrographic competence.

As for point (2), ("knowledge of the main topics covered in class") the main evaluation criteria are:

  • Terminological accuracy and correct use of the specialized lexicon;
  • Ability to use the basic petrographic knowledge during the argumentation;
  • Focusing on the question = don't go off topic
  • Logical sequence in reasoning;
  • Ability to take a critical position regarding one's own arguments and those of others;
  • Creativity to solve interpretation issues.

Teaching tools

  • Video Projectors supporting Power Point presentations
  • Devices for remote teaching
  • Hand-sized samples
  • Thin sections
  • Polarizing Optical Microscopes
  • Mineral and rock collections of the Museo di Mineralogia Luigi Bombicci

Office hours

See the website of Roberto Braga