OdontoliteAlso known as Bone turquoise, this beautiful rock is formed in the depths of sedimentary s
OdontoliteAlso known as Bone turquoise, this beautiful rock is formed in the depths of sedimentary stacks, as bones like this fossil jaw are preserved for the aeons during the process that turns their surrounding sediments into rock. Teeth are the most common part of the skeleton that turn into odontolite, hence its name.It was long thought to be coloured (like turquoise) by copper, and when analysis failed to reveal its presence, by the iron phosphate mineral vivianite (see http://tinyurl.com/mnvy6vx). Recent research has shown that it usually consists of crystals of blue apatite (see http://tinyurl.com/l5rzpag), coloured by trace impurities of manganese, though some turqouise (copper phosphate) specimens are known, like this sample.It is formed by heat and copper bearing fluids passing through fossiliferous rocks and is often found near copper deposits in arid areas, part of the same pule of mineralisation that left the ore grade concentrations behind. In the old days it was called occidental turquoise to distinguish it from the oriental version which is a clay rock coloured by copper oxide, and occasionally the former has been erroneously (or fraudulently) sold as the latter. They can be told apart by their hardness, with the oriental version being harder. The most famous locality is in France, especially in the southwestern Languedoc region, where they accumulated in river sediments derived from the erosion of the nearby Pyrenean chain.They preserve bone structure beautifully and are much sought after by palaeontologists. This kind of mineral replacement is known as pseudomorphing, with the new mineral taking the shape of the previous one, in this case a jawbone. This specimen was mined in the Bolivian altiplano and was once the jawbone of an animal some 20-40,000 years ago. It measures 4.2 x 3.0 x 2.1 cm.Image credit: Rob Lavinsky/iRocks.comhttp://bit.ly/2eaZJvbhttp://www.mindat.org/min-32412.htmlA paper on how it forms, paywall access: http://bit.ly/2dq03F1 -- source link
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