The most important theme is that the logo be simple, elegant and trustworthy. Selling higher end jewelry is all about trust.
I've uploaded some photos of what tanzanite looks like.
You are welcome to try experiment with a theme around gemstone/s or potentially metal although this is not imperative because most of the exclusive jewelry companies have very plain logos. That being said, I'm not looking to replicate but rather be innovative/clever.
Concerning certain things I've had in mind, I think playing with the "o" of maslov with a round cut stone being looked from the top or maybe the "v" for a stone being looked at the side.
It would be cool to have almost a logo for every theme of jewelry, for example the "o" to look like a tanzanite for the tanzanite jewels catalogue, or the "o" to look like a diamond for the daimond jewels ctalogue, or the "o" to look like a emerald for the emerald jewels catalogue etc.
The logo must be on a white background so it's important that it stand out.
The color theme for the marketing will most like be hues of violet, purple, blue and grey. The jewelry pictures will be floating on a white background and the color scheme will be complimentary as opposed to over whelming.
Good luck and have fun!!