Why do minerals have colours?

Because some of you asked during ‘La Fête de la Science’ in Paris why minerals have different colors I decided to write this post about it.

First of all, I need to define the electromagnetic spectrum, and the energetic distribution of electromagnetic waves. But what is a wave? Let’s make that clear by looking at waves in the ocean (figure 1).

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Figure 1: Ocean waves (source: http://www.livescience.com/38361-how-do-ocean-waves-form.html)

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