Cordierite

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Cordierite is a silicate mineral that forms in metamorphic and igneous rocks, boasting vibrant blue to violet hues. This highly pleochroic mineral stands out as one of the most striking examples of its kind. Geologists use the term "cordierite" to refer to this specific mineral. When cordierite is transparent and of exceptional quality, it's known as "iolite" in the gem and jewelry industry. Two older names for cordierite are "dichroite" and "water sapphire." The name dichroite comes from the Greek words "di," meaning two, and "chroma," meaning color, due to its unique pleochroic property. Water sapphire is also linked to this phenomenon, as a specimen can appear as a deep blue like sapphire when viewed from one side, but turn clear like water when rotated.