Explore key concepts in mineralogy and crystallography through this comprehensive 33-minute video lecture. Delve into the four major symmetry operations, including mirrors, rotation axes, centers of symmetry, and rotoinversion axes. Learn about twinning in minerals, covering twin elements and various types of twinning such as contact twins, penetrated twins, and multiple twins. Gain a thorough understanding of Miller indices for crystal planes, starting with an explanation of mineral lattices and unit cells before progressing to practical applications. Discover the importance of Miller indices in determining d-spacing and their role in X-ray diffraction (XRD) and Bragg's Law. This informative lecture serves as a foundation for upcoming topics in XRD and optical mineralogy, providing essential knowledge for Earth science enthusiasts and students alike.