Of the impurities of the ore the wolframite (tungstate of iron and manganese) is the most troublesome, because on account of its high specific gravity it cannot be washed away as gangue.
Tungsten is found as wolframite in Stevens county near Deer Trail and Bissell, in Okanogan county near Loomis, in Whatcom county near the international boundary, and (with some scheelite) at Silver Hill, near Spokane.
Tungsten is found in wolframite in Boulder county.
Important mines of gold and silver, considerable deposits of wolframite, valuable ores of molybdenum and vanadium, and quarries of onyx marble, are also worked.
There is some roofing slate along the Rogue river, natural cement, nickel ore, bismuth and wolframite in Douglas county, gypsum in Baker county, fire-clay in Clatsop county, borate of soda on the marsh lands of Harney county, infusorial earth and tripoli in the valley of the Deschutes river, chromate of iron in Curry and Douglas counties, molybdenite in Union county, bauxite in Clackamas county, borate of lime in Curry county, manganese ore in Columbia county, and asbestos in several of the southern and eastern counties.