Mottramite on calcite rhombsMottramite is part of what is known…

Mottramite on calcite rhombs

Mottramite is part of what is known as a solid solution series, when there exists a continuum of chemical composition between end members within a mineral family. In this case the end members oscillate between lead and copper vanadate, formed when primary ore deposits are altered by the passage of oxidising mineralised fluids. Mottramite is the copper rich end member, as evidenced by the gorgeous green colour, while orangey brown descloizite (see http://bit.ly/2wcLVI9 and http://bit.ly/2uLvIJx) is the lead rich one. The stalactite in this unusual piece from the Tsumeb mine in Namibia (see http://bit.ly/1c2CjkD) has grown on a matrix of calcite and been subsequently encrusted with gemmy transparent rhombs. The specimen measures 3.1 x 2.9 x 1.5 cm
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Loz

Image credit: Spirifer Minerals

http://www.mindat.org/min-2792.html
http://www.galleries.com/Mottramite
http://webmineral.com/data/Mottramite.shtml

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