Blue John (aka Derbyshire fluorspar) which only is found in one place in England, Castleton. It was "unimprovable", which aligned with English values at the time - it could not be dyed or convincingly imitated. And it was specifically ENGLISH. It rose to promincence during periods of anti-import sentiment and pride in British manufacture. 1" tall and 1 1/8" wide (not including metal ring at top). Rustic, hand-carved and polished. Hard to date - maybe c. 1880 to be safe. "Geologic" quality with layers.