Tanzanite

Tanzanite is a subtype of the mineral zoisite that ranges from violet blue to blue violet. Only one place in the world, Tanzania's Merelani Hills, where it gets its name, is mined for commercial purposes.

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Pleochroism, or a gemstone's capacity to exhibit various hues when viewed from different crystal angles, has a significant impact on tanzanite's look. Soon after tanzanite was discovered, pleochroism in the stone was described in scientific papers. The pleochroic hues of the gem were characterized as "red-violet, deep blue, and golden green" in an article published in American Mineralogist in 1969. As a result of heat treatment, the majority of gems nowadays have less or no yellow-green or brownish pleochroic hue, allowing the blue and violet to stand out.