Symmetry Operations, Types of Twinning, & Miller Indices of Crystal Planes- Mineralogy | GEO GIRL

Understanding symmetry elements and operations, twinning in minerals, and miller indices of planes is important in mineralogy and crystallography. This video covers the 4 major symmetry operations (mirrors, rotation axes, centers of symmetry or inversion, and rotoinversion axes), twinning (twin elements such as twin planes, twin axes, and twin centers, and types of twinning such as contact twins, penetrated twins, and multiple twins), and miller indices of cleavage planes (first I go over what a mineral lattice and unit cell is then a miller index, how to figure out a miller index, then we do practice!), lastly we go over the importance of miller indices (determining d-spacing with miller indices and x-ray diffraction (XRD), as well as Bragg's Law!). This lecture leads into the upcoming lectures on XRD and optical mineralogy.

Reference: Chapter 5 in Earth Materials by Cornelis Klein https://amzn.to/3EEoyGI

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0:00 4 symmetry operations
0:38 mirrors and rotation axes
5:06 centers of symmetry or inversion
6:17 rotoinversion axes
7:01 twinning crystals
10:14 cleavage planes & miller indices
11:41 unit cells in crystal lattices
14:06 miller indices explained
18:15 miller indices practice
27:54 why do miller indices matter?
30:37 upcoming content!
32:31 bloopers

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