Bisbee turquoise is revered world-wide for its exceptional beauty and value.  These stones are from the famed Lavender Pit copper mine in Bisbee, Arizona.  The turquoise itself was often found in the tailings from mining operations, which ceased in the mid 1970s and the mine closed.  The fact that no more turquoise can come out of the mine only has added to its value.
 
This cabochon is $3.65 / carat and measures 18 cm x 3 cm.  It weighs 5.3g, or 26 carats.