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Crystal lab
Short lessons acted out on crystal models: things a photo cannot show. Every 3D crystal here is a model, not a photo.
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Light and fire
Light slows down and bends as it enters a stone; the higher the refractive index, the more. Violet bends a little more than red, so white light fans out into colours: the “fire”. The spread is the dispersion.
n 1.550 · dispersion 0.044. Red and violet leave the prism 1.98° apart (colour spread drawn 8× wider so it can be seen).
Refractive index: middle of the sourced range. Dispersion: the standard B–G value (430.8 to 686.7 nm) from gemmological tables.