Royston is an historic turquoise district in Nevada featuring many mines. The history is found in Turquoise in America Parts 1-3.
 
This cab weighs 42 carat and measures 5.5 cm X 2.5 cm X 3 mm. It is priced at $15 a carat or $630. It is not treated and is backed. I have assigned a TG of 87 or VHG. I purchased this cab from a Japanese master lapidary.