Birthstone jewelry makes a perfect gift.  There's no worrying about whether the color is right or if the size is correct.  Rings can easily be sized up one or two sizes or down at the local jeweler.  Many online jewelry stores offer rings in several sizes and even show you how to measure for the correct size.

Jewelry doesn't have to be horrendously expensive if you know where to shop.  How about a one carat diamond ring for just a bit more than $200.00?  Don't think that's possible?  Well it is when the diamonds are set in sterling silver instead of platinum, or white gold, and there are 168 diamonds adding up to a total weight of one carat instead of 3 or 4 bigger diamonds. 

If bracelets are more your type of gift, surprise her with an emerald bracelet of nearly seven carats set in vermeil (gold overlaid on silver) for less than $200.  The bracelet is a basket weave setting allowing more light to interplay and bounce off the emeralds highlighting their intense green color. 

When on the hunt for jewelry bargains, shopping at a reliable jeweler, whether offline or online is important to make sure you receive the quality you've paid for.  Buying second hand birthstones or birthstone jewelry from an auction site, or in person at a second hand shop or pawn shop is risky.  Many times only a certified gemologist is able to separate the real birthstones from the imposters.

Seeing a foil backed gemstone or a closed back setting is a dead giveaway that the stones are glass rather than real.  However some of the more brilliant crystals don't require either the foil backing for their brilliance and are often set in open pronged settings. 

Doublets

Colored gemstones are valued on their color and size.  The deeper the color and closer to the spectral hue -- the color you see in a rainbow -- the more valuable. Since most jewelry is viewed from the top of the stone, placing a deeply hued slice of the same gemstone on topic of a paler gemstone infuses the entire gem with a deeper color.  For example:  beryl, the mineral emeralds are made of, comes in shades of pale yellow to dark green (as well as red but that's another story).  A slice of grass green beryl on top of a pale yellow faceted stone makes the entire stone look greener.  The slice is easily hidden by the cut of the stone.  In fact unless you know the doublet is there it's difficult to spot.

Nearly every gemstone, including opals, can be faked with a doublet.  The gemstone is real so testing methods won't show it to be a fraud. The value can be completely misrepresented.

Synthetics

Many gemstones, especially the more expensive ones, rubies, sapphires, and emeralds can be created in a lab at a much lesser cost than natural stones.  There is nothing wrong with a synthetic gemstone as long as it's not misrepresented as a natural gemstone.  It's difficult to tell the difference even for a jeweler.  Most lab created stones are without any flaws and are nearly perfectly colored.  Lab stones created to intentionally be sold as natural are created with flaws and imperfections.  Most synthetic stones are created in the United States, transported to the Far East, sold in the Far East because that's where most rubies and sapphires are mined and sold and then imported back to the United States or to Europe.

Simulated Stones

Stimulated stones are not made of the same chemical composition as natural stones.  Simulated pearls are not pearls at all for example but usually plastic or mother of pearl over plastic.  Cubic zirconia stones are sold as simulated diamonds and when colored as simulated rubies, emeralds and sapphires.  Again this is perfectly fine as long as the stones aren't misrepresented as being the real deal.

False Categorization

Certain stones are associated with certain colors: topaz is yellow or blue, amethysts are purple, emeralds are green, rubies are red, and sapphires are blue.  However there are many gemstones that come in a variety of colors.  And that's great if you have your heart set on blue gemstones, for example, but can't afford sapphires.  Blue topaz is available at a more budget minded cost.  If you love rubies, which can be very expensive, you may be able to afford garnets which are less expensive. 

The problem is when the less expensive stone is sold as the more expensive stone.  Another take on this is to rename the less expensive stone as a variety of the more expensive stone.  Below are a few such examples:

Arkansas diamond is quartz

Matura diamond is zircon

Evening emerald is peridot

Oriental emerald is green sapphire

Slocum opal is plastic

Majorca Pearls are plastic

Australian ruby is garnet

Water sapphire is iolet

Madeira topaz is citrine quartz

Shopping at an established online jewelry shop with a strong reputation is critical. A beautiful bracelet with gemstones graduating from yellow to pink to orange accented with white gemstones should be labeled as sapphires and zircons (which is a natural gemstone not to be confused with cubic zirconias) not as some sort of colored diamonnette bracelet. 

A beautiful ring with a large yellow stone surrounded by multi colored gems is actually a 7.45 ct center Citrine stone surrounded by tsavorites, rubies, and sapphires.  It shouldn't be misrepresented as a yellow topaz ring surrounded by emeralds, rubies, and sapphires.

Birthstone jewelry is a nearly perfect gift. Know what you're getting and get what you pay for.