General Geology Course 1 PDF - Yahia Fares University

Yahia Fares University MEDEA Faculty of Sciences Department of Agronomic Sciences GENERAL GEOLOGY First-Year Agricultural Engineering (2024-2025) Geology course 1 Geology is the science that studies the Earth, its composition, structur...

Yahia Fares University MEDEA Faculty of Sciences Department of Agronomic Sciences GENERAL GEOLOGY First-Year Agricultural Engineering (2024-2025) Geology course 1 Geology is the science that studies the Earth, its composition, structure, the processes that shape it, and its history. More specifically, it focuses on the formation of rocks, minerals, soils, as well as phenomena such as earthquakes, volcanoes, erosion, and plate tectonics. Main objectives of the geology module:  Understanding geological processes ,  Knowledge of the Earth's structure ,  Water resource management ,  Natural risk assessment 1- Minerals - Notion of crystallography and crystal system - Mineralogy: mineral definition and classification 2- Rocks - Magmatic rocks - Sedimentary rocks - Metamorphic rocks Introduction Planet Earth is made up of several layers of viscous or liquid rock, with different and complementary properties. The inner and outer core The outer and lower mantle The Earth's crust. Each Of these three types of layer has its own structure, thickness and temperature (fig. 1), The Earth's crust is the outermost part of the Earth, the part we know best because it is here that people, plants and animals live, and it represents just 2% of the planet's volume. Mainly made up of solid rocks, which are materials generally formed from an assembly of minerals and which have a certain statistical homogeneity.  Earth's crust: Solid outer layer of the Earth, 5 to 70 km thick.  Upper mantle: Part of the mantle below the crust, 0 to 410 km deep, more rigid.  Lower mantle: Deeper part of the mantle, extending from 410 to 2,900 km, viscous.  Outer core: Liquid layer of iron and nickel, extending from 2,900 to 5,150 km, generates the magnetic field.  Inner core: Solid centre of the Earth, composed of iron and Figure 1: Internal structure of the nickel, extending from 5,150 to Earth 6,371 km. 1- Minerals A mineral is a natural chemical species most often presented as a crystalline solid. The classification is based on their chemical and crystallographic characteristics. Figure 2: Minerals 1-1- Crystallography concepts and crystal system a- Crystallography concepts The term Crystallography of the latin crystallus crystal (crystal object, ice,...), derived from the ancient Greek krystallos ice Crystallography is a science that studies the crystalline substance at the atomic scale, as well as its formation, growth, external form, internal structure and physical properties of crystallized matte. The crystalline state is defined by a periodic and ordered character at the atomic or molecular scale. b- Crystal system A crystal is a polyhedral solid (a three-dimensional geometric shape with flat faces that meet along straight edges), with a regular and periodic structure, formed by an ordered set of a large number of atoms, molecules or ions. It can be described by translation following the three reference directions of a basic entity called the unit cell. Absence of reticular structure characterizes the amorphous material, which are constituted by a chaotic arrangement of their atoms which gives a, disordered internal structure and whic do not carry a natural geometric shape glasses represent a well-known example of amorphous material (Fig. 3) Figure 3: Amorphous solids and crystalline solids A crystalline material may be either: A single crystal (single crystal) for example quartz, calcite, diamond. A polycrystal or agglomeration of small crystals (steel sample) ,  unit cell, pattern, lattice and crystal structure:  unit cell: From a geometric point of view, with two dimensions, the unit cell is the smallest parallelogram which is enough to describe the plan (fill all the plan without leaving gaps). That is to say the minimum volume of a crystal that allows to judge the atomic structure of the entire volume. In three dimensions, theunit cell is the smallest entity (the smallest volume) corresponding to a parallelepiped, it is defined by three vectors a, b and c (the periods following the axes ox, oy and oz, respectively) not coplanar and three angles α, β and γ (fig. 4). Figure 4 : Unit cell crystal  Pattern: A pattern is an atom (ion or molecule) or a group of atoms of the same or different nature that is repeated, periodically, following the three directions of space to describe the crystal. The crystal lattice : it is a purely geometric notion, it consists of the set of points, ends of all possible translation vectors.  Crystalline structure: In a simpler way one can put: Crystal structure = The crystal lattice + Pattern (Fig. 4) , b- Crystal system From the elementary crystal unit cell, we can describe in a simple way the crystalline systems existing in nature. The 7 crystalline systems are generated by the different possible combinations on one side between linear parameters (a, b and c) and on the other side between angular parameters (α, β and γ). Thus in nature, only 7 basic polyhedral forms allow to build the structural infinity of minerals. However, if their forms are similar from one mineral to another, they vary in size. Length, width, height of a unit cell is specific to each crystalline chemical form (fig.5).