When buying a pendant, what do you think is the best gemstone to give as a present in a new or fairly new relationship? Does it say romance? Does it say you're paying attention to what she likes, her personality, or her style of dress? Does it say you're giving her a token of affection appropriate for something new or does it possibly communicate you're trying to "buy her attentions" by going too far? Her birthstone is a great idea, again, as long as it's not something out of proportion to the seriousness of the relationship (like a diamond, ruby, emerald, or tanzanite).
Notice that this is list is mostly for pendants. Because gemstones in rings are more easily damaged, many stones, such as topaz, aren't great choices.
(Having trouble uploading photos, so there will be updates to come.)
http://www.ranker.com/list/gemstones-best-first-gift/admiralcrunch,
Carnelian
While some people think of carnelian as having a sweet, softer personality, because it's often found in sedate pink cameos, most traditions see it as a highly suggestive stone, especially when it's the bright cherry red it's originally known for. (Consider what it might represent to someone who takes the chakras seriously.) The pinkish-orange to coral color is much easier to wear for a variety of skin tones and a variety of outfits than similar flashy vitreous gems. Meanwhile bolder and darker red carnelian is striking against both dark skin and very pale skin. Either way,in the event your girlfriend takes gemstone symbolism to heart, know that this stone says you have very heated intentions. ;)
Moonstone
Moonstone is a great early present as it's romantic and tender. Good for a present for college-age romances or older, but it might seem a little too passionate for new high school sweethearts. Moonstone solitaires tend not to be that expensive and look attractive on about every skin color except the palest. It's also shows thoughtfulness since it's not usually a stone that immediately comes to mind nor is it the easiest stone to find in stores.
Amber
This is a great present for high school romances (or college and up). Most amber will have visible impurities or "bubbles" but it is possible to find inexpensive amber on sites like Silverspeck that will have a uniform coloration.
Jade
Certain shades of green are considered a "neutral" like white or black, so a green jade is a good present because it takes a bit more originality to think of it than more common stones, and it will look good with most outfits. Jade can be a little suggestive, but it depends on the tradition. If considering the chakras, green jade is a much sweeter and friendlier gesture than something like carnelian. Also, for someone who dresses conservatively for work, a strand of green jade beads and freshwater pearls (freshwater is much less expensive than natural sea pearls or cultured pearls) would look great. By the way, typically jadeite is a light green, and that's the variety that will "go with just about everything". The other jades like nephrite or maw-sit-sit are usually darker, more distinct, and more expensive.
Redheads often look great in green, so a jade cabochon (a smooth, rounded stone) pendant set in yellow gold would likely be perfect.
Amethyst
Amethyst is eye-catching, even in smaller stones, and generally not confused for other gems. It's also the birthstone for February. It may not be the most original choice, but it's a good option if you don't know someone's tastes well. I've never heard anyone say "ugh, amethyst" and it does look beautiful on most skin tones. It's probably your best bet if you want to hear an excited intake of breath when she opens the box.
Onyx
(Onyx actually isn't always black, but a variety of banded agate. However, you will mostly find onyx sold as a solid black stone, so that's what I'm talking about here.) Onyx can be a fantastic stone for someone who dresses elegantly or conservatively. It's definitely a good present before a formal event that won't break the bank.
Onyx set in silver or other white metals is usually preferred over gold. Onyx in larger or free-form cuts can also be nice for someone with exotic tastes.
Smoky Quartz
This is a gemstone that looks excellent on most skin tones, but I can think of a few hitches. The word "quartz" often makes people think "cheap" because quartz is the second most common mineral. Even though amethyst and citrine are also types of quartz, any kid can go outside and grab a rock that will likely contain milky quartz. So this gem loses a degree of specialness. Second, it loses out to rose quartz because there's a possible reaction of "gee, you gave me a brown gemstone? Thanks." Even though it's beautiful, you might think of emotions that you associate with colors like red or purple, then compare them to brown. You can spin it as "It's not brown, it's champagne" or "You're so beautiful you don't need something bright and flashy."
Next, even if she loves your choice, it's still not a stone that indicates romantic intention. It's more of a friendly stone, that you'd give a family member. There are still reasons it could be a hit. Women with fair skin, brown hair and brown eyes often look stunning with smoky quartz or a combination of smoky quartz and citrine. You might get points for originality and for paying attention to what she would look good in. Someone who favors chocolate-tones or conservative tan, beige, or taupe would probably like this as well. As you might guess, this goes with a lot of autumn wardrobes, so jewelry stores tend to carry more in the fall.
Rose Quartz
This is sweetly romantic and affectionate. This can be perfect for high school sweethearts, college students or young people in general, but for someone mature, it might be too sweet or unsophisticated. It can be hard to find in stores and high quality rose quartz can be expensive. Often looks good on blonde woman or women with pale complexions, and women who dress in soft colors. One problem with rose quartz is that it tends to be seen as a "daytime" stone instead of something for evening wear, and like most quartz varieties, over time it can fade in sunlight.
Lapis Lazuli
A lot of people love the deep blue of Lapis. It's not an easy stone to find in stores, however. The darker blue gives it a warmer tone than blue topaz or turquoise. If you notice that your girlfriend/romantic interest likes larger jewelry, this is a great starting point. You might also consider other opaque stones later.
Multi-gem Bouquet Piece
This is kind of a safe present, but can be a good choice, especially if it's something she might open in front of family and you don't want to be too forward (They are especially popular for Christmas as they are cheerful and colorful.) The message this sends is often a much sweeter "Hi, I'd like to get to know you" sentiment than a large solitaire gem which might say "it's time to get serious".
Most inexpensive pieces will have a combination including amethyst, citrine, peridot, and garnet or maybe all of them. (If they include sapphire, it's almost always man-made sapphire, but that's a stable stone, so I don't care if you don't.) If it includes white stones, that's fine if they are white topaz or actual diamond, but not really if it's "CZ" (cubic zirconia) because CZ becomes cloudy in time. It's rare to get the highest quality stones in a multi-gem piece, so I wouldn't expect rich color saturation, but it's definitely a bonus if the piece possesses it, especially the amethyst. Also, check to see if the saturation of same-species gems match each other.