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General Overview

• Course: General Geology II (G102)

• Audience: 1st Year Students (2024-2025)

• Main Topics Covered:

  • Minerals

  • Rocks (Igneous, Sedimentary, Metamorphic)

Minerals and Rocks

• Minerals

  • Quartz

  • Granite (Igneous Rock)

  • Feldspars

  • Sandstone (Sedimentary Rock)

  • Gneiss (Metamorphic Rock)

  • Micas:

    • Muscovite

    • Biotite

Course Structure

• Syllabus Overview

  • Part I: Crystallography

  • Part II: Mineralogy

  • Part III: Petrology

    • Igneous Rocks

    • Sedimentary Rocks

    • Metamorphic Rocks

Crystallography

I.1 Define Crystallography and Crystal

• Crystallography:

  • A branch of science studying crystalline matter at the atomic level, both chemically and naturally formed.

  • Focuses on mineral crystals, analyzing morphology (external form) and internal structures.

• Crystal:

  • A solid material with an ordered internal structure (atoms, ions, or molecules).

I.2 Unit Cell

• Definition:

  • The smallest group of similar/different elements arranged in a 3D geometric shape.

• Example:

  • The cubic structure of NaCl (Halite) and Fluorite made from cubelets.

I.3 Crystal Lattice

• Crystal Lattice:

  • Regular repetition of unit cells in three dimensions.

• Space Lattice:

  • Points in space representing each atom in the unit cell.

• Types of Lattices:

  • Bravais Lattice: Same surroundings for each lattice point.

  • Non-Bravais Lattice: Different surroundings for at least some lattice points.

I.4 Crystalline vs Amorphous Substances

• Crystalline Substance:

  • Has ordered internal structure, may have crystal faces, sharp melting points, and constant temperature during cooling.

• Amorphous Substance:

  • Lacks ordered structure and crystal faces, no definite melting point.

I.5 Crystal Parts

• Components of a Crystal:

  • Crystal Faces: External smooth surfaces.

  • Crystal Edges: Intersection lines of neighboring faces.

  • Solid Angle: Meeting point of three or more faces.

  • Interfacial Angle: Angle between neighboring faces, consistent irrespective of size.

I.6 Elements of Symmetry

• Importance:

  • Internal symmetry affects external forms in perfect crystals.

• Types of Symmetry:

  • Plane of Symmetry: Divides crystal into two identical halves.

  • Rotational Axes of Symmetry: Imaginary lines allowing crystal rotation through various angles.

    • Two-fold (180°), Three-fold (120°), Four-fold (90°), Six-fold (60°).

  • Center of Symmetry: Inversion point where symmetrical points on opposite sides exist.

I.7 Elements of Crystallization

• Crystallographic Axes:

  • a-axis: Front to back.

  • b-axis: Left to right.

  • c-axis: Top to bottom (vertical).

• Crystallographic Angles:

  • Alpha (α): Between b and c.

  • Beta (β): Between a and c.

  • Gamma (γ): Between a and b.

I.8 Crystal Form

• Types of Crystal Forms:

  • Open Form: Faces cannot completely close in all directions (e.g., pinacoid, prism).

  • Closed Form: Can completely enclose the crystal (e.g., bipyramid, cubic forms).

• Classification:

  • Simple Crystal: One closed form.

  • Compound Crystal: More than one form in regular arrangement.

I.9 Crystal Systems

• Classification Criteria:

  • Number and lengths of crystallographic axes.

  • Interaxial angles.

  • Elements of symmetry.

• Seven Crystal Systems:

  1. Cubic (Isometric)

  2. Tetragonal

  3. Orthorhombic

  4. Monoclinic

  5. Triclinic

  6. Hexagonal

  7. Trigonal

I.10 Summary of Crystal Systems