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The Mineral Identification Key |  |
Minerals with a iridescent luster
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| Covellite develops a deep blue iridescence, 4cm across, Montana |
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| Labradorite, 20cm wide, Madagascar, Seaman Museum specimen |
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| Iridescent pyrite, 4cm across, Australia |
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| Iris agate, 8cm across, Brazil. The "iris" effect (the pink/green) rainbow effect is due to diffraction of the light by the fibrous silica in the agate. (This is best viewed with a light source behind the agate slab). The bands can be up to 17,000 per inch to cause this effect. |
