PargasiteThe beautiful green crystal sitting pretty on its matrix of marble was born in the intense

PargasiteThe beautiful green crystal sitting pretty on its matrix of marble was born in the intense heat and pressures associated with the building of the Himalayas. As the sea that formerly separated the continents closed, the limestone that was formed from the ooze was thrust up and baked into the pure white marble. The impurities within were distilled out by hot fluids and recrystallised as a wide variety of minerals, from corundum (sapphire and ruby) and spinel to rarities like Painite. These transformed sea bottoms host gems as far apart as Afghanistan (eg the ruby mines of Jagdalek), the Pamir mountains of Tajikistan and the Mogok stone tract of Burma whence came this piece.The mineral is part of a large family called amphiboles, which are common in both igneous and metamorphic rocks. Named in 1815 after its type locality (ie from which it was first described) in Finland, it forms in high temperature metamorphic events such as mountain building or in the rings of baked and stewed in mineral rich fluids rocks that occur around granites (known as contact metamorphic aureoles, they are made of a rock known as hornfels, or skarn if the granite intruded into carbonate rocks such as limestone or dolomite).It is also sometimes found in a type of lava called Andesite (after the mountain chain where it is ubiquitous) that is associated with subduction volcanism. As the slab sinks into the mantle, the water baked out of the minerals as the heat and pressure increase rise and cause the mantle wedge above to melt and produce silica enriched magma. It is also found in the shallow mantle, where it acts as a mineral store of water, though it changes below a depth of 90km. Zones of mantle enriched in it are easier to melt and release magma.As well as these lovely gemmy deep greens, colours range from brown to opaque dark green or black. Other locations for the gemmy stuff include the Luc Yen/Yen Bai marbles of Vietnam, almost always associated with deep red spinels and the Hunza valley in the mountainous Gilgit region of Pakistan and Nova Scotia in Canada. Dark crystals of this mineral are also associated with the ruby in zoisite (see http://on.fb.me/1FmQdFr) found in Tanzania. The specimen in the photo measures 7x6x3 cm.LozImage credit: Carion Minerauxhttp://www.mindat.org/min-3119.htmlhttp://www.gemdat.org/gem-3119.htmlhttp://bit.ly/1FlpkCAhttp://bit.ly/1eGSWnChttp://bit.ly/1SIBGhxhttp://bit.ly/1HZJLZahttp://bit.ly/1GM64Tu -- source link

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