The Turquoise Group .Turquoise identification and nomenclature is
compounded by several problems. Turquoise is part of a group of 3
minerals ( Hydrous Aluminum Phosphate and a solid solution of [
Copper - Turquoise ], [ Iron - Variscite ], [ Zinc - Faustite ] .
So Turquoise can be a chemical solid solution containing Copper,
Iron, and Zinc in varying amounts . The Hydrous Aluminum Phosphate
allows substitution of some of the ( Copper and/or Iron and/or
Zinc ) .
Variscite may be interspersed with other phosphate minerals - (
Crandallite, Wardite, Gordonite, and Hydroxylapite )
If this is not confusing enough, there are several other minerals
Prosopite, and Howite are used as substitutes , with and without
Stabilized Turquoise, Treated Turquoise, Reconstituted Turquoise,
and Imitation Turquoise, are all separate considerations which add
to the confusion.
Faustite is yellow - apple green colored stone.
Variscite is yellow - green to blue green.
A retired lapidary dealer from Farmington N.M. told me that if it
would cut and polish, was moderately durable, and in demand, it was
likely sold as turquoise.
Gemstones of North America Vol 1 - John Sinkansas. *
Gem and Lapidary Materials - June Culp Zitner *
Color Encyclopedia of Gemstones - Joel E. Arem *
Gemology II edition - Hurlbut & Kammerling **
Dana’s Mineralogy IV edition - E.S. Dana
- in print or easily available, ** in print but expensive,
Google does not have all these subjects treated well , if at all.
You expected an easy answer about a gemstone , used from earliest
times, available world wide, has such variety and is still so much
in demand ? It is my favorite gemstone.