Blue Gem is the name of several turquoise claims. The most famous is the Blue Gem mine near Battle Mountain NV. The story is told in Turquoise in America Part Two, 1910-1990.
 
This cabochon weighs 42.5 carats and measures 3.5cm X 2.5cm. It is not treated and backed. It is priced at $10 a carat or $425. I have assigned a TG of 78 or HMG, High Mid Grade. This stone was cut and purchased from Jim Elquist who mined the turquoise.