Double sulphide Sitting atop a sizeable oblong crystal of the common lead sulphide mineral galena is a clump of small crystals of a very rare cobalt nickel one called Siegenite. First described from a mine in Germany in 1850 and named after Siegerland, the area in which the mine was located. It forms in veins precipitated from the hot mineralised fluids circulating through the Earth that ferry around, concentrate and deposit so many of the metals which we rely on for all the clobber we need in order to live in the style to which we have become accustomed. It is also found in Bosnia, the Czech Republic, Scotland, Uganda, the Katanga Provincee of the DRC, Japan, Karlgoorlie in Western Australia and the USA. It forms a solid solution series with pure cobalt and nickel end members. Like may sulphides it is fairly soft, 5 or so on Mohs scale, and tarnishes on contact with air and humidity to a violet grey. The 3.7 x 2.3 x 1.8 cm example comes from the Missouri lead belt of the USA. Loz Image credit: Rob Lavinsky/iRocks.com https://www.mindat.org/min-3655.html
