Most important, check over the terms used for substitute gems, especially those of any gems in which you might be interested. Although no reliable jewelry would knowingly pass off one gem for another, if you are going to shop around you are going to have to expect to run into jewelers who may be less fussy.
Keep in mind that you cannot always tell what gem is by looking at it. Emeralds are green. Also, Tourmalines are green, and that name itself comes from the Singhalese word for mixed gems. Smoky quartz can outwardly resemble the more precious smoky topaz. Then, there are the gems of which few consumers have heard, like spinel.
There is no rule of thumb of what you can expect to pay. Any price list today is out of date before it is printed. The only way you can tell what is a fair price is to ask jewelers. If you don’t have a regular jeweler whom you trust, it is even more important to shop around and check the prices of particular gems. If you want smoky topaz, look at smoky topazes in as many stores as possible to get a general idea of the current price, although prices will vary with size and quality as well as setting. Still, you can get fair idea of fair topazes, or other gems, as possible.
Although the terms “precious gem” and “semi precious gem” have little meaning as the prices of all jewelry increase, the less expensive gems are probably safer buys from the point of view that there is less reason for anyone to try to sell a gem that isn’t what it is supposed to be. However, some inexpensive gems, such as turquoise and zircon, can have nature improved on by various kinds of treatment, and spinel and garnet can be synthetic.
Another problem in buying jewelry with gems is that the gems are already set. Once a gem is in the setting, you may not be able to see all the inclusions, nor may an appraiser, because the setting can hide them. A setting can also make up for imperfect cutting. That doesn’t mean you should buy only unset gems. The average person can be as taken in by unset gems as by set ones. It does mean that where you buy can be more important than how to buy.
Still and all, there are some precautions you can take in shopping around and looking at gems. These precautions hold particularly true for diamonds, which are most common gem purchased, and for few other stones.