Jewelry store margins will vary quite a bit from store to store and from product to product. As a rule, the percentage of the sales price required to replace the goods goes up with higher priced items. That is to say that the markup percentage on inexpensive items like watch batteries and silver charms is way better than on expensive items like big diamonds and Rolex watches. This makes sense but it leads to a widely held misconception about the profits associated with owning a jewelry store and the belief that stores double and triple their materials costs. On inexpensive items the markup can be 3x or even 5x while on diamonds where the stores cost is over, say $20k, consistently getting a 25% mark is doing pretty well.
It’s worth noting that some stores have a habit of putting price tags on things that don’t really represent their prices. What they call their regular prices may not be the prices that they are expecting to get when they finally find a customer.
Lastly, it’s worth noting that stores will often deliver benefits, and incur costs, that are not part of stone itself. This includes things like trade up programs, convenient display, financing, warranties, helpful salespeople, access to designers, lab services, etc. When you consider questions of markup, you must consider markup from what. ‘Free’ addons aren’t really free.