Place a sample on a piece of patterned paper or card and slide it across the page. The image should appear to spring to the surface. Experiment a little! Are there any angles where the effect doesn't seem to work? Does the pattern appear clearer in some places than others? What happens if you place this on top of a coloured picture? What happens when you place it on writing -- is it a mirror image or does it just show the image underneath? What happens if you place this on top of a torch, or a phone light?
Selenite is a form of gypsum, it is formed of long thin crystals which act as a natural light pipe. It reflects the image internally and projects it to the surface. The image should look physically closer. This is not true fibre optics as the material does not display total internal reflection. The sample must be tilted by 20° before the effect is visible.
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