Tungsten or its ore, especially as a commercial commodity.By 1907 most of the gold mining was replaced by tin and wolfram....
It's then balanced with heavy inserts of wolfram (the principle ore in tungsten) on both the heel and toe.
Karens also make their living by fishing in coastal areas, working in tin or wolfram mines, and gathering forest products like rattan and honey.
Origin
Mid 18th century: from German, assumed to be a miners' term, perhaps from Wolf 'wolf' + Middle High German rām 'soot', probably originally a pejorative term referring to the ore's inferiority to tin, with which it occurred.