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| June 2004
Gemstones/Gemology A Tree Runs Through it Gemological features create an interesting story for ametrine These examples of ametrine, that curious combination of citrine and amethyst, illustrate two gemological features: one common, the other rare. Color Zones After you recover from the stunning light effects of Dalan Hargrave’s prize-winning ametrine sculpture (right, top), you’ll notice the unusual color zoning patterns typical of ametrine. A type of twinning known as Brazil law twinning is partially responsible for the color zones. (Twinning refers to two crystals that grow together but with different lattice directions). It’s thought the triangular yellow sections (citrine) contain more trace elements of iron-causing color and the purple ones (amethyst) less. Bolivia is the only known source of commercial ametrine in the world. The Tree Miners at the Anahí mine that produces ametrine have uncovered only a handful of these interesting gemological nuggets. The one they allowed Professional Jeweler to examine (right, bottom) features a dendrite inclusion, very rarely seen in massive quartz such as ametrine but quite common in agates, a microcrystalline form of quartz. Close examination of the ametrine reveals a small fissure along the base of the crystal, and it’s here where the mystery begins to resolve itself. A minute, partially healed fissure extends from the surface entrance through the length of the crystal. At some time during the crystal’s hydrothermal formation, traces of another mineral, possibly manganese, entered through this opening, oxidized and formed the dendritic pattern. (Iron oxides tend to have yellow or orange dendrites). Here, the internal “life” of the gem mimics the forested terrain above the mine where it was found. For more information, see the Gemological Institute of America’s quarterly journal, Gems & Gemology, Spring 1994, pp. 4-23, for a feature on ametrine and the Anahí mine. – by Robert Weldon Photos by Robert Weldon
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