The opinion on this site;
Comments for Gold Ring Hallmark states that-" The red stone is most probably a garnet. "
From website:
"Sounds like beautiful art nouveau men's gold ring you have acquired. Art Nouveau Jewelry was produced between 1895 -1910, when jewelry of the late 19th century was ripe for change.
The Cabochon stone cut has a smooth rounded surface and was used in antiquity and continued until the 15th when it was superseded by faceted stones and was was revived during the Art Nouveau era. The red stone is most probably a garnet.
These dates also coincide with the sponsor's mark of "an anchor tipped to the right and the letter K" used by Ripley-Howland Mfg Co. on 10K Gold Rings, Manufacturing Jewelers, Boston, MA, and New York, NY, USA - ca 1887 "
Nice finds p-12!