Aperçu des sections

  • Preface & Objectives

    Preface All solids, whether natural or artificial, that surround us originate from a well-arranged microscopic component called a crystal. The growth, synthesis, and maintenance of crystalline matter are intrinsically linked to the atoms that compose it. Their orderly arrangement results from the laws governing their stability, as well as the physical and chemical properties that distinguish crystals from one another. The science that deals with everything related to crystals is called crystallography. Numerous fields are interested in the study of crystals, including inorganic and organic chemistry, physics, geology, metallurgy, biology, and medicine. This highlights the importance of studying crystals in our daily lives, as nearly all our products and raw materials are crystalline. For example, rocks are composed of minerals, while minerals are formed from an assembly of crystals, which are made up of atoms (motifs) organized into geometric systems called lattice networks.

    Mineralogy, the science that studies minerals, relies heavily on crystallography, as certain properties of minerals are linked to the formation of crystals in their deposition environment. Students are expected to understand all crystal systems, their geometry, symmetry elements, and the various modes and classes to which they belong. They must also grasp the fundamental concepts of crystallography, which are taught in the first year of geology.

    The first part of the course, titled Geometric Crystallography, focuses on explaining the fundamental concepts of crystallography, such as laws, crystal structures, and their components (lattice and motif), as well as the different bonds formed. It also interprets the notion of symmetry, classes, and associated operations and describes certain properties related to the arrangement of atoms and molecules within a three-dimensional unit cell. The second part, titled Crystal Optics, interprets the instrumentation used for observing and measuring crystals, such as X-ray diffraction and emphasizes understanding the interaction of light with crystalline bodies.

    Objectives Understand Crystal Systems, where students should be able to identify and describe all crystal systems, their geometry, and their symmetry elements. Also, students should interpret symmetry operations, crystal classes, and their applications in crystallography

    Master Fundamental Concepts, so students must grasp the basic principles of crystallography, including lattice structures, motifs, and atomic arrangements and help to understand the physical and chemical properties of crystals and how they relate to atomic arrangements.

  • Chapitre I

    La cristallographie permet de représenter la structure cristalline d’un minéral suivant un arrangement en trois dimensions de ses atomes et elle classe les cristaux selon des règles géométriques.


  • Chapitre II

    La structure interne d’un cristal est représentée suivant ses motifs chimiques (atomes) et ses maquettes géométriques (réseaux cristallins). Une structure cristalline et un réseau cristallin sont deux notions différentes. Une structure cristalline est composée d'atomes, d’ions ou de molécules alors qu’un réseau cristallin est un modèle mathématique infini de points qui ont la même orientation et qui sont occupés par un groupe d’atomes reproduit périodiquement dans l’espace.


  • Chapitre III

    Les mailles cristallins constituantes un réseau en trois dimensions représentées par les périodicités ( a, b et c ) correspondent aux parallélépipèdes et il existe sept types de mailles cristallines représentatives des sept grand systèmes cristallins (Fig. 34). Ces systèmes cristallins sont obtenus par les combinaisons possibles entre les paramètres linéaires (a, b et c) et les paramètres angulaires (α. β et γ).


  • Chapitre IV

    La conservation d’un cristal de sa structure régulière est liée à l’arrangement particulier et ordonné des atomes suivant des interactions établies entre eux garantissant leur cohérence. Nous pouvons constater trois liaisons chimiques ou de fortes intensité (ionique, covalentes et métalliques) et deux liaisons physiques ou de faibles intensité (liaison hydrogène et de Van Der Waals)