The Subway (or should it be sewer?) GarnetThough this whopping crystal has been given a plethora of

The Subway (or should it be sewer?) GarnetThough this whopping crystal has been given a plethora of names (including the Manhattan and Kunz garnets), it’s most evocative name is a misnomer, changed by Victorian sensibilities, since it was in fact excavated while digging a sewer. The latter name might have been more appropriate, since the gem started life as disseminated atoms amongst the ooze lying over the volcanic rocks at the bottom on the Iapetus Oceanic plate, which once separated America from Europe some 600 million years ago. The sediments were eroded from the continent of Laurentia and the fine particles settled out of the water to the deep bottom.It was found in a rock called the Manhattan schist (see http://on.fb.me/1OKsOYH) that underlies the skyscrapers of the island. As the ocean closed some 440 million years ago, and an island arc (volcanoes overlying a subduction zone, where oceanic crust is sinking into the mantle) crashed into Laurentia, it squished up some of this ooze and basalt and welded it to the continent.The Appalachians started growing, and the intense heat and pressure transformed the rocks into different minerals, in a process called regional metamorphism. Some of the new minerals included garnets, and the rock became foliated, a series of lines developing in the rock in response to directed pressure. Finally a granite intruded in, baking the schist some more, and this garnet was found in the metamorphic halo surrounding this interloping rock.The specimen was found in 1885, near the intersection of 35th Street and Madison Avenue. The size of a bowling ball (15cm across), it weighs around four kilos. After some time as a media sensation, it faded from the swift changing attention of the city, and ended up as a doorstop in the Department of Public Works.It was bought by a dealer, and ended up in the hands of George Kunz, a mineralogist who was a curator of the American Museum of Natural History’s collection, and a famous dealer in his own right who helped JP Morgan amass the collection that would later form the core of the museum’s own (the mineral Kunzite is named after him, see http://on.fb.me/1Xm9G4H). The Subway is a typical reddish brown almandine garnet, coloured by iron. The crystal faces on the dodecahedron are well formed with clear edges, except where it was once attached to the matrix.LozImage credit: American Museum of Natural History.http://bit.ly/1hWI0TThttp://bit.ly/1RYeXfDhttp://bit.ly/1LOllW1http://nyti.ms/1PCq6o8 -- source link

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