This is an extremely old and interesting ring, made by rustic techniques not seen much, if at all, after World War I. It may be substantially earlier than that.
Turquoise stones first appeared in Native American silverwork in the 1880s, a couple of decades after a few tribesmen learned to make silver jewelry. It wasn't produced on a commercial scale until around 1920, when tourists of the "Fred Harvey Era" began visiting the Southwest by railroad. Tools were generally primitive before then and most silver was from coins melted down. Rapid advances in quality during the 1920s, more turquoise from new mines and the availability of sheet sterling from around 1930 accounted for the differences we see in newer jewels, which are generally hallmarked and often maker-marked.
Here the only marks we see were made by files, hammers and casting in sand or tufa rock. Both the setting and the turquoise cabochon show the surface irregularities we expect from early work and are, like all the first pieces, of Navajo style. Tribal distinctions didn't arise until many decades after Navajos passed silversmithing skills along to their Zuni and Hopi neighbors.
The stone, as you see, is a particularly luscious one -- certainly natural, grown greener with age and loaded with copper matrix that looks characteristically Bisbee (called the "Tiffany of Turquoise"). That mine has been closed for ages, as have all others from which this could conceivably have come.
About a U.S. size 5 now, the ring could be easily altered either way, since the dual shank unites at the back. The face measures about 5/8 by 5/8 inches and the stone about 1/2 by 3/8 inches, sitting high in a tall collet against a flat background with a dimensional edge patterned to look like a twist. The finer workmanship of the band suggests that it might be a later replacement for a simpler one broken long ago. We haven't cleaned the ring at all, leaving to its next owner the decision on how far to go with polishing.
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