Color Change Tourmaline (Dravite)

Usambara Effect Color Change Tourmaline

Color change Dravite crystals from the Umba Valley of Tanzania.  The crystals appear green, but in transmitted light, exhibit a sharp color change to red when the crystal reaches a certain thickness. In the photos where the crystals are backlit, you can see this effect - in the thicker zones the color changes to red, and along the thinner edges, the color remains green. This color change (which is different from the "alexandrite effect", which is color change dependant on type of light) has been called "Usambara effect", after the nearby mountains where they are found.  The vast majority of this material is only suitable for gemstones and good crystals are rare.

Nchongo, Umba Valley, Tanzania

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