RockglowWe have a complex rock here from the Franklin mine in New Jersey (itself named for Benjamin

RockglowWe have a complex rock here from the Franklin mine in New Jersey (itself named for Benjamin Franklin), where we have white Calcite and Willemite (see http://bit.ly/2GhhXnj), red Zincite (see http://bit.ly/2swKnHX) and black cubes and octahedra of Franklinite (see http://bit.ly/2CrkoS0) disseminated into the matrix amongst the other minerals. The rocks of the Franklin mines are probably skarns (see http://bit.ly/2siU5gK and http://bit.ly/2nJRB6G), that formed when granites intruded into (in this case) half billion year old Cambrian/Ordovician limestones and baked them in their mutual juices until all sorts of interesting contact metamorphic minerals form in zoned aureoles around the cooling intrusion. There is some debate about the origin of the deposit, with the other possibility describing a metamorphosed ocean floor zone, in which the original bodies were deposited as zinc rich sediments on the margin of a long gone oceanic basin that was then metamorphosed in a subduction zone as one plate slid under another into the depths of the mantle a billion years ago, before rising again as a diapir (see http://bit.ly/2EtoLla) into marbles (metamorphosed limestone). Two of these minerals are displaying beautiful fluorescence under UV light, the calcite glowing a lovely orange and the Willemite green, allowing easy separation between these two white minerals.This phenomenon arise when some of the electrons in the outer shell get excited by absorbing light, especially at higher energy ultraviolet (UV) wavelengths. These electrons jump up to a higher energy state when excited. They fall back to their initial equilibrium energy state when the excitation, such as a UV light, is switched off. While doing so they give off their energy at a wavelength specific to the impurity’s electron energy jump. This is what we see as fluorescence, and the emitted wavelength is always longer wavelength and lower energy than the exciting one, so invisible (to us) UV light will make a stone fluoresce in a lower energy part of the rainbow. Please be careful playing with UV lights if you try this at home, as the higher energy ones can damage the retina. The piece is some 15cm across.LozImage credit: LGF Foundationhttp://www.lgffoundation.com/ -- source link

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