Like USAFRet said, we'd need to know what lens mount your camera uses in order to recommend a particular lens. Generally though what you would be looking for is a prime macro lens. (Prime means it cannot zoom, but prime lenses are much sharper than zoom lenses.) These lenses are able to focus at a much closer distance than a standard lens. Excellent macro lenses are obviously quite expensive but decent enough ones aren't terribly bad. For example, on a Canon EOS mount you have the 50 mm f/2.5, 60 mm f/2.8, and 100 mm f/2.8 (non-L) as reasonably-priced macro lenses. The 50 mm is the least expensive of the bunch at about $300 MSRP but the 100 mm f/2.8 (~$600 MSRP) is probably the most popular as it gives greater magnification.
Alternatively you could take advantage of a modern DSLR camera's high-resolution sensor to use an inexpensive standard prime lens and then crop out the excess stuff you don't want in the picture. A ~$100 "nifty fifty" (the least expensive prime lens sold by the maker, usually a 50 mm f/1.8) stopped down to f/3-f/4 or so is usually extremely sharp and close to as good as what you'd find with the super-pricey glass. They generally have a minimum focal distance of 1.5 feet as opposed to a handful of inches for a real macro lens. However, you can easily crop out the extra background that shows up in your picture. You do lose some ability to do very "arty" shots shooting in this manner but I have a hunch you're more concerned with getting good pictures of jewelry to post online for sales purposes. This is personally what I do, I use a $90 Canon EF 50 mm f/1.8 II stopped to about f/4 and crop out the background for my "macro" shots. You still end up with about a 3000x2000 or so image which is plenty large.