Iolite (cordierite)

Iolite is a gem variety of cordierite, an aluminum and magnesium silicate with the formula (Mg,Fe)₂Al₄Si₅O₁₈. It is known for its remarkable pleochroism, revealing shades of violet-blue, light blue, gray, or yellow-brown depending on the crystal's orientation. Formed primarily in metamorphic rocks, iolite appears in prismatic crystals and is often associated with quartz, feldspar, or garnet.

Sometimes called "water sapphire," it is prized in gemology and mineralogy for its deep colors and fascinating optical variations.