So let's talk a bit about decorative mosaics.
The mosaic above is a decorative wall panel. It was inspired by a necklace found in King Tut's tomb (image at right, photo by Araldo de Luca). While the necklace itself is not purely decorative, my rendition of it is.
I was attracted to the repetitious and almost geometrical composition of the lotus flowers and buds, as well as the lovely composition of the fully opened flowers. I chose the color palette to go with a particular room. No deep meaning here, just wanted to create a decor item for the house.
If you're not sure if a mosaic is decorative or not, explore the intention with which you made it. A still life, for example, may not be expressing a deep meaning, but it is probably expressing a point of view. Did you make the still life of flowers merely to decorate a wall or to match the furniture? Or were you trying to communicate your experience of those flowers?
Likewise, a pet or human portrait—while it may not be a philosophical statement, is most likely an attempt to communicate aspects of its subject.
The above image shows two necklaces: A stunning mosaic pendant by Margo Anton, and a non-mosaic piece that I bought at a museum gift shop in Mesa, AZ.
Since Margo was one of the first to submit for my book, I am pretty comfortable saying that the necklace she made is a decorative mosaic. Her intention was to make something beautiful that someone would find joy in wearing. I can personally attest to the success of her intention.
It's pretty clear that the other necklace's intention is to make a statement. While it is not mosaic, it can hopefully be a helpful example.
So, is all mosaic jewelry decorative? No. As the creator, your intention answers the question. After that, it truly is in the eye of the beholder as to with what level of art it will be embraced.