Show SAPPHIRE MINE IN MONTANA the sapphire workings at yogo gulch montana are being gradually developed into a great and permanent mining industry says george F kunz in a forthcoming report on precious stones published by the united states geological survey taken as a whole the yogo togo dike is perhaps the greatest gem mine in the world it is about four miles long on the surface and being a true igneous dike descends to an indefinite depth it is estimated that the entire content of workable sapphire bearing rock would a approximate ap pp proximate roxi mate cubic yards A mining plant is now being erected which will quadruple the output the stones obtained are not of large size they range from culs used for watch jewels and other mechanical purposes to gems averaging when cut from half EC a carat to two or three carats barats and rarely up to five or six As gems they are brilliant free from flaws and of good color ranging from light shades to the rich deep blue of oriental sapphires sapp hires the yogo crystals have an advantage for mechanical uses over east indian stones in their form which is largely short prismatic or with flat basal terminations and hence they need much less cutting for such purposes as watch jewels the gems are sent to amsterdam for cutting and yield from two fifths to one half their weight in finished stones |