Benitoite on natrolite
While we have covered California’s state gemstone before (see http://on.fb.me/1KSaNnm), we just couldn’t resist sharing this wonderful 8x8x5cm slab of deep blue crystals on the zeolite mineral natrolite. Their formation is complex, involving hydrothermal fluids passing through two separate rock formations lower down in the sedimentary stack, mobilising a variety of elementsalong the way and precipitating them as a rare assemblage of minerals. It is ultimately a child of tectonic metamorphism that occurred when chunks of crust and upper mantle were sucked down with the subducting oceanic plates off the west coast of America and bouncing back up to the surface due to their buoyancy.