The Time StoneThis gem quality specimen was photographed in the Natural History Museum of London. Em

The Time StoneThis gem quality specimen was photographed in the Natural History Museum of London. Emerald, our classic green gemstone, is not a mineral on its own; rather it is a specific variety of the mineral beryl, a beryllium-aluminum-silicate mineral. The mineral beryl can have many colors – in fact, it can also be a gemstone with a pale blue color in the form of aquamarine. The classic emerald gets its color from substitution of the element chromium into the structure. Chromium is a metal ion with d-electrons, so like the color we saw earlier in spessartine, electrons in the d-orbitals can jump from low to high energy positions when they’re exposed to visible light. Chromium substituted into minerals commonly produces brilliant green colors – other minerals, including fuchsite, variscite, diopside, and tsavorite garnets can all find their green color partially or fully produced by chromium.As with iron in amethyst, the chromium is not specifically found in the pure mineral formula for beryl. Instead, the chromium has about the same charge and about the same size as one of the elements in the mineral – typically the aluminum. Therefore, it can swap places with the aluminum and be present in the mineral as an impurity. Even though the chromium only makes up a small portion of the atoms of the mineral, its absorbance is strong enough to impart the color to this gemstone.-JBBImage credit: https://flic.kr/p/agwux5References:https://geology.com/minerals/beryl.shtmlhttp://minerals.gps.caltech.edu/COLOR_Causes/Metal_Ion/index.html -- source link

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