Morganite with KunziteSitting on its 27x20cm matrix of Afghan Quartz and Clevelandite feldspar, we h

Morganite with KunziteSitting on its 27x20cm matrix of Afghan Quartz and Clevelandite feldspar, we have two minerals born in the dying remnants of cooling granites. The pink to peachy variety of beryl called Morganite *the pink crystal in the foreground) is coloured by trace impurities of manganese or caesium. It was first discovered in Madagascar and named after the banker and mineral collector J.P. Morgan in 1910 by Tiffany’s famed gemmologist George Kunz (after whom Kunzite is named). It grows in pegmatites, those crystallised rare element rich juices left over when granites stew as they cool and crystallise, concentrating rare elements that won’t fit into quartz or feldspars. It can grow to quite large sizes, the US record holder was found in Maine, and weighed in at 23kg. It varies in hue from lilac or violet, through pink to a delicious peachy orange. As for all coloured gems, saturation and tone of the hue are the most important quality factors, followed by clarity (freedom from inclusions) and beauty of cut. Since morganite’s hues are poorly saturated and light toned (ie quite pale and pastel), larger sized gems are needed to display the colour to its full beauty. They are usually quite high clarity, and have strong pleochroism, so must be cut in the right orientation to display the best colour.Quality stones are rare, so rare in fact that they are comparatively cheap, since supply is not high enough for large volumes of mass market calibrated stones. It is often heat treated to remove a yellow component to the colour, and has been irradiated on occasion to induce colour. Common sources are Madagascar, Brazil, California, Afghanistan and Mozambique.Sitting in the background is a purple crystal of Kunzite, the beautiful pink to violet variety of the lithium silicate pyroxene group mineral spodumene. It is a relatively recent addition to the gem inventory. It was first described in 1902 by the gem and mineral dealer G.F. Kunz (who worked, amongst others, with Tiffany’s, the Smithsonian and assembling J.P. Morgan’s world class mineral collection), after its initial discovery in California famous Pala district pegmatites. While this example does not display them, crystal surfaces are often covered in triangular arrowhead shaped etch pits where the crystal was dissolved by hydrothermal fluids during its residence in the air.The mineral is strongly pleochroic, displaying three different colours depending on the orientation from which it is viewed. This is due to the different pathways rays of light take within the crystal when they are refracted and split into 3, resulting in different absorptions and residual colours visible to the eye. As a result, gem cutters have to be sure to cut it in the correct orientation to display the deeper violetish hue through the top table facet rather than the pale pink to colourless one. Though it has decent hardness (6.5-7 on Mohs scale), faceting is complicated by the mineral’s perfect easy cleavage, where the crystal splits along lines of weakness with fewer atomic bonds in the crystal structure.The best examples come from the pegmatite fields of Nuristan in Afghanistan, and display strong violet, pale pink and pale green shades. Other localities include Madagascar, Brazil and the USA. Most kunzites are quite pale, and more saturated shades (due to substitution impurities of manganese in the crystal structure) are quite rare. It is one of the few gems available in large sizes relatively inclusion free at reasonable cost. Quality depends on depth of colour and clarity, and the larger the stone, the deeper the colour. Crystals in the Black HIlls of Dakota have been found up to 14.3 metres long. The largest cut gem weighs 880 carats and is held by the Smithsonian Institution.The colour can slowly fade in direct sunlight, so wearing it for prolonged periods under Sol’s rays is not advised. Some specimens have been heated or irradiated to enhance the colour.LozImage credit: Stuart Wilenskyhttp://www.mindat.org/min-2783.htmlhttp://www.jtv.com/library/morganite.htmlhttp://www.gia.edu/morganite-descriptionhttp://www.gia.edu/morganite-quality-factorshttp://www.gemdat.org/gem-2783.htmlhttp://www.gemsociety.org/info/gems/morganite.htmhttp://www.mindat.org/min-2289.htmlhttp://www.gemstone.org/index.php…http://www.minerals.net/gemstone/kunzite_gemstone.aspxhttp://www.gemologyonline.com/kunzite.html -- source link
Tumblr Blog : the-earth-story.com

More pics about