Ok. I tend to use books for geologists rather than "new age" texts for identifying stones. I find that geologists take better (and more accurate) pictures. Another way, if you are really stumped, is to find a rock shop that caters to rock hounds (people who hunt rocks) and you can have an expert identify it for free.
I also have several on-line resources I'd like to share.
Here's a page that has pictures of various commonly found stones. They may not be useful, but it can help.
Further, you can use google as your guide, and look up "healing gemstones" and start searching through the various links at the various pictures of stones and see the resemblance. Here's an example of the kind os site you want to find on google:
http://store.stormsong.org/cart/section ... ---tumbled
You want to look at several sites like this, as they have different "takes" on what a particular stone looks like.
If you figure it out generally, then you can look at various examples of the kinds of stone you have specifically at this site:
These guys have great photos, but cover more kinds of stones than a casual user would want. Search for the common stones first.
The really nice thing about the mineral galleries link is that it gives you notes as to how scientists told various stones apart back in the 19th century. This is handy if you are a looking at the thing in your home. However, some of them aren't useful, like "reacts thusly to hydrochloric acid". They also tell you about look-alikes for that stone, and some practical means to tell them apart. This site is almost more useful when you already know what stone you have, but I have had luck with identification on this site.
However, sometimes it really does take an expert. If they bring out the Loupe to figure out what kind of stone it is, you are vindicated. Sometimes the only way to tell certain kinds of stones apart is to look at it's texture magnified.
And if you still can't tell: it's either an agate, a jasper, or a form of quartz. Those are the most common for those kind of stone jars.
Interestingly enough, in one place I once frequented had Wulfenite in their $2 tumbled stone jar. Score!
Also, sometimes the stone that resists identification can be one of your more powerful allies. Ask the stone what it does, or how it can help you as a magickal practitioner. Talk to your stones, and you will be rewarded.
Further, those books that tell you what they do are always general guidelines, not specific to that individual specimen you are holding in your hand. Each is an individual.
EDIT: It occurs to me that this thread will never be out of date. Why not make it a sticky in this topic?