From multimedia.lycos.com

Prior to this, this site has focused mainly on the geological aspect of diamonds. However, I couldn't leave out one of the most important things -- what to look for in a diamond when buying one! Ask any diamond expert, and they'll tell you to look for the 4 c's. That is, the cut, clarity, carat weight, and color of the diamond. However, many jewelry stores will often try to rip you off or make up names and facts about diamonds! Be Careful!

Below is my advice on selecting a diamond (keep in mind, this is for a more important diamond, like one for an engagement ring)...

The most important one is the cut. This is what gives the diamond its "sparkle." Most of the sparkle you see in a diamond is due to the cut (clarity and color help out only a little here). Diamonds can be cut in many different shapes also, such as the round (or brilliant) cut, emerald cut, princess cut, and so on. The round, or brilliant, cut will be more sparkly when compared to the other shapes of comparable diamonds.

For the cut, the types that you'll see (the ones that are good enough to market) are fair, good, very good, and excellent cuts. Most jewelry stores only carry good cuts and sometimes very good cuts (they usually don't have excellent cuts). Be careful when talking to sales people, as they general say that the cut they have is the best (when indeed it's not). To check this, ask for a certified diamond. Certified diamonds are graded by an independent gemstone grader, and they'll say if they're fair, good, very good, or excellent. Often stores will charge you more for certified diamonds, but they really try to rip you off and sell you a "good" diamond for the price of an "excellent" diamond. Also, some jewelry stores will try to rename cuts to names like masterpiece and so on, which is why you again have you be careful and request a certified diamond.

Good cuts do look very nice. Most diamond engagement rings that you see contain "good" cuts, because very few people know that there are better cuts. Excellent cuts will show more sparkle, and you'll notice it a lot, but it all depends on how much you want to spend and what you care about the most in a diamond.

Polish and symmetry also come into play with sparkle (although minimal), and most places don't tell you about this. It has the same ratings (fair, good, very good, and excellent). You probably won't be able to tell much of a difference here between a good and an excellent, but there will be a minimal difference (light can travel through it better when it's more symmetrical).

Clarity is another important part of a diamond. Almost all diamonds have inclusions (little things inside of a diamond that happen when diamonds are formed). Most people don't know this, but probably everyone you know of has inclusions in their diamonds, but the extent of these vary greatly. They go from invisible to the naked eye to visible to the naked eye. The scale for this is FL (flawless), IF (internally flawless), VVS1 and VVS2 (very very small inclusions), VS1 and VS2 (very small inclusions), SI1 and SI2 (small inclusions), and I (inclusions). FL and IF diamonds (flawless) are VERY rare and VERY expensive. Unless you want to spend over $10,000 dollars on a small diamond, you probably shouldn't look at these. Besides, no one can tell the difference between flawless diamonds and VS and SI diamonds usually. For your sake, you should look more at VS and SI's. A VVS doesn't have much of a difference compared to a VS, and some SI's you can get that look like VS's. S o let's focus on VS, SI, and I. Almost all VS diamonds have inclusions that you can't see to the naked eye. Under a 10x microscope, a trained gemologist might be able to see something VERY tiny. As for SI diamonds, some of them are invisible to the naked eye (almost all). Under a 10x scope, a trained gemologist would be able to see something small a little easier than he/she would with a VS. Stay away from I's, as those you can see with the naked eye (from the top of the diamond). Sometimes they'll be black lines or dots, while other times they'll be cloudy parts on the top of a diamond. Sometimes you might be able to find an alright I diamond and save a lot, but it's all up to you.

Most important in all of this is to ask for an eye clean diamond. Eye clean means that you can't see any inclusions with the naked eye. Almost all VS diamonds are like this, and some SI diamonds are like this. If you find an SI diamond that is eye clean, you should go with that, because you'll save a couple hundred dollars for something that you won't be able to tell the difference with between a VS and SI. Other times with an SI diamond, you'll see nothing from the top of the diamond (the most important part), but you might see something REALLY faint on the side depending on the light you're in. A small secret is that most diamonds that people have usually have this, but not many people notice it.

Now about color, the scale is D E F G H I J K L ... D, E, and F are colorless, while G, H, and I are near colorless. Anything beyond that has a faint tint of yellow. Most people can't tell the different between a colorless and near colorless diamond. You might be able to tell the difference if you hold them side by side, but even then maybe not. Most engagement rings are usually about an H in color (near colorless). I'd recommend not going past an H in color, as an I sometimes picks up a slight hint. An F or a G might be a good deal, as it'll be basically colorless and cheaper than a D or an E. A lot of people are picky about color, so the price might change for something that you really can't tell a difference with.

As for carat weight, I'm sure you know about this. The larger the weight, the bigger the diamond. Personally, I think people focus on this too much and always try to go for the biggest diamond. In reality, a .5 diamond might be as expensive as a 1 carat diamond if the .5 diamond is a really good quality. Small diamonds that are of excellent quality will get noticed more than a larger diamond that isn't so nice.

Lastly, you might hear about fluorescence. This isn't really a big deal at all, and most jewelry store workers don't know what this is. Basically, if you put the diamond under a black light, it's how much of a blue tint you'll see. Some salespeople say that it makes the diamond cloudy and less sparkly, but this isnt really true (although in extreme cases, it might look a bit different in sunlight). It's usually only the tint of blue you see under a black light. It's not a big deal at all, but if you want no tint, then pick a diamond with no fluoresence.

That's about all there is for what to look for with a diamond. Try to focus on eye clean diamonds in the SI clarity area (you can go VS if you have the extra money and don't want to bother looking for an eye clean SI diamond), D to G color, and very good to excellent cut.

Another secret that most people don't know about is that you can save a couple thousand dollars by shopping at other places like www.bluenile.com or other online stores. They often offer excellent cuts at a great price. Often, they'll have excellent quality diamonds that you can find for cheaper than comparable diamonds that are of a lesser quality at jewelry stores. Jewelry stores often try to trick you by offering a "good" quality for a similar price, while bluenile.com will offer you an "excellent" quality for the same price if not cheaper.

Sometimes jewelry stores will sound like a good deal with their package deals of free resizing and such for a couple years or the rest of your life, but in reality, a resizing only costs about $15 at a normal store ($20 tops), and you probably won't be resizing a ring much throughout your life.

Hopefully, you know have a better understanding of diamonds both geologically and in terms of picking one out!

A chart for the clarity of a diamond.

From http://www.diafinance.com/aboutdiamonds.html

A color scale for diamonds.

From http://www.diafinance.com/aboutdiamonds.html