Unit 4.1 – Glide Planes in Crystals (I)
Further material/links:
VESTA file of orthoclase with embedded glide planes
Explore the the glideplanes in orthoclase – a feldspar mineral. Can you find out, what type of glide plane is present?
Unit 4.2 – Glide Planes in Crystals (II)
Unit 4.3 – Screw Axes
Further material/links:
Olafur Eliasson
Link to the homepage of the Danish-Islandic artist Olafur Eliasson
A musical helix
Tones can be represented as a helix as well. This helix makes one turn with each octave.
Clever arrangements of notes result in the so-called shephards tones. They appear to descend or ascend continuously in pitch. An illusion to our ears.
Visit the link for further information about this phenomenon.
Unit 4.4 – Screw Axes in Crystal Structures
Further material/links:
A different interpretation of the 3(2) screw_axis in order to emphasize the similarity to a 3(1) screw
CIF file of the element Tellurium
Unit 4.5 – Space Groups and Space Group Symbols
Unit 4.6 – International Tables and The Spacegroup Pmm2
Further material/links:
Crystallographic Space Group Diagrams and Tables
Space Group Visualizer
Eckhard Hitzer and Christian Perwass worked on visualising point and space groups using the visualisation tool CLUCalc. This software implements Geometric Algebra, which allows for a direct implementation of symmetry operators in the algebra – great tool!
Unit 4.7 – The Space Group Pmm2 (II)
The Fascination of Crystals and Symmetry 