Thomsonite on HeulanditeWe have here two minerals of the zeolite family that forms when heated hydro
Thomsonite on HeulanditeWe have here two minerals of the zeolite family that forms when heated hydrothermal convection cells circulate through rock (usually in the bubbles and cavities in basaltic lava though it has turned up now and again in granitic pegmatites) picking up and precipitating elements depending on the ambient chemical conditions as it does so. The brown potato like spheres are the first named in the title and the pinkish matrix the second, which I have already covered (see http://bit.ly/2BQR9Zr). Like many such it forts what is known as a solid solution series, in which two or more elements can substitute for each other at the same spot in the crystal lattice due to their similar size and e4lectronic affinities (in this case strontium and calcium). Advanced testing is needed to reveal which element is dominant and how it should be properly described. Its type locality (from which it was first described in 1820) is in Scotland, and it was named after a chemist hailing from that part of the British Isles who first analysed and described it formally. Colour ranges from white or brown through to greenish, yellowish or reddish and it tends to form in long thin bladed crystal that often internest into spherical radiating sprays like the examples in the photos. While soft (5 on Mohs scale) it is occasionally faceted for collectors. Localities include the Faroes islands, several places in the USA, Russia and the Deccan Trapps of India, source of many zeolite mineral specimens in the global gem market. A unique massive variety with banded colouring is found on the shores of Lake Superior which is often tumbles into pretty pebbles or cut into dome shaped cabochons. The 7x6.5 cm specimen in the photo came from Maharashtra state in India.LozImage credit: LGF Foundationhttps://lgfmuseum.org/https://www.mindat.org/min-28896.htmlhttp://www.galleries.com/Thomsonitehttp://bit.ly/2llt4Tvhttp://www.minerals.net/mineral/thomsonite.aspxhttp://bit.ly/2C40h0F -- source link
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