Arts & Crafts jewelry was usually one-of-a-kind pieces. The movement started in England, where most pices were done in silver. Motifs were usually natural or abstract, using enamel and semi-precious stones to emphasize the style/shape of the piece instead of bling. Finishes were often dull as to not just "shine" but to contribute to the piece as a whole. It was different from the Art Nouveau work in that it had different motifs - definitely either more conventional ones or abstract pieces. Can be mistaken for it though.
English designers include:
C.R. Ashbee (considered a founder of the movement)
Birmingham guild of handicraft
CH Horner etc, etc
In the US, it was called The Arts and Crafts Revival and the jewelry tended much more to the abstract. Chicago was the major center for this movement. Perhaps the most famous of the groups was The Kalo Shop. There is a book on my wish list "The Chicago Metal Smiths" by Sharon Darling. It is a 1977 book but a great reference. They concentrated on non-precious metals like brass & copper for their pieces.
Unfortunately, many of the artists and workshops putting out this jewelry failed because the production was time-intensive and not suitable for mass production. Also, tastes were moving much more to the Deco style.The years are about 1880-1910. Some of the older jewelry (not the 1940s stuff) that we call "modernist" is Arts & Crafts.
If you search for work by the Kalo Shop, Jane Addams, The Chicago Arts and Crafts Society or Florence Koehler, you will find excellent examples of American A&C jewelry.
I have a couple of pieces I think are A & C but one is marked with an unreadable sig and the others aren't't marked -