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The simplest way to think of what is happening is when light which is a self sustaining electromagnetic wave enters a medium made up of atoms. The electrons of those atoms will oscillate and re-radiate at the same frequency. This will change the resulting EM wave vector. The positive nuclei are too massive to be affected.
Ordered crystals can have properties such as birefringence or polarisation. This is due to the non isotropic arrangement of atoms and hence electrons.
Cubic lattices of course are isotropic. Such as Fluorite. Glass is isotropic due to its random structure.
Metals attenuate light because of the free electrons.
Bert
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