HydroxylherderiteThe apatite group of minerals (see bit.ly/2akYWkg) encompasses quite a varie
HydroxylherderiteThe apatite group of minerals (see http://bit.ly/2akYWkg) encompasses quite a variety of species, with this variant being a beryllium rich calcium phosphate. Like in the rest of the family, ions of similar size and charge such as OH and fluorine commonly substitute for each other in the crystal lattice alongside the beryllium and calcium, with the final product a result of the composition of the mother fluid from which the piece in question crystallised.Colour varies from yellow through brown to green, though colourless specimens also turn up. It forms in granitic melts, usually crystallising in pegmatites, the last fluid rich parts of the magma that have concentrated all the rare and unusual elements that do not fit into the more common minerals’ lattices. It forms in the late stages of crystallisation, often in cavities as water and steam rage together in the magma’s last dying gasps. Another formation method is by alteration of minerals such as beryl, and precipitation from in veins.It was discovered in Saxony in 1828 and named after a local mining official (a bit like Goethite was named after another better known mining official, this time from Weimar, see http://bit.ly/2aVMCHN for a biopic). The hydroxy was added when this variant was discovered in 1894, and most specimens labelled Herderite are in fact this version.Locations include Brazil, the Czech Republic, Finland, Germany, Italy, Namibia, Russia, Spain, England and the USA, though this 4.7 x 4.0 x 2.3 cm rare green specimen sitting on a crystal of shorl (black tourmaline) was mined in the Gilgit region of the Hindu Kush in Pakistan. The last photo shows it fluorescing in UV light, whose high energy excite electrons into higher orbits, and when they fall back (since what goes up must come down unless it is held up) they emit lower energy light in the visible range of frequencies.LozImage credit: Rob Lavinsky/iRocks.comhttp://www.mindat.org/min-1962.htmlhttp://bit.ly/2aDZYrQ -- source link
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