Glowing CalciteThis crystal of calcite from the Apache Mine in New Mexico is colorless when it is ex

Glowing CalciteThis crystal of calcite from the Apache Mine in New Mexico is colorless when it is exposed to visible light. However, when exposed to ultraviolet light as in the frame on the right, the crystal lights up, in this case showing two colors. Each of these colors represents an interesting optical effect occurring due to the underlying chemistry of the crystal.The diffuse reddish to pinkish color throughout the grain is an example of fluorescence. This property of a mineral is basically the conversion of one type of light to another; in this case, ultraviolet light is being converted to emitted visible light.That conversion occurs thanks to the elements lead and manganese substituted in minor amounts in the calcite structure. Lead substituted into calcite is able to absorb light energy in the ultraviolet. We don’t see the included lead as a color because that absorption is outside our visible range, but lead is a common substitute in calcite and that substitution commonly excites fluorescence under UV light. Other elements can also substitute in calcite and serve this role; longer wavelength UV light can cause other elements to serve as the absorber for fluorescence.The manganese substituted into calcite is the other part of fluorescence. The lead in the calcite absorbs the ultraviolet light then passes some of that energy on to neighboring atoms of manganese. That energy excites electrons in the manganese, and when the electrons return to their normal state they give off light with a characteristic wavelength depending on the environment where the atoms sit. Manganese substituted into calcite gives off light in the visible range at wavelengths that our eyes recognize as pink to reddish.The bluish light is the typical light given off by calcite due to phosphorescence. Unlike fluorescence, phosphorescence is a property of some minerals where the light continues being given off after the UV source is removed. The source of phosphorescence in calcite is a little less well known, but experiments show that it vanishes as the crystal is heated, implying it is due to damage in the crystal that is repaired as the crystal heals. A missing element or a dislocated bond in a crystal can serve as a site where electrons get trapped and an electron stuck in the structure of a mineral can also give off light as energy is passed to it; in this case, that light appears blue. It’s probably not a coincidence therefore that much of the blue light seems to occur near the edges of this grain where dislocations and damage are more likely.-JBBImage credit: Hadley Paul Garlandhttps://flic.kr/p/6eknH7References:http://www.fluomin.org/uk/fiche.php?id=157http://bit.ly/1T1uLSC -- source link

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