The Low-Down on the Gem That Will Last Forever

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Find out everything you need to know about diamonds.

This post by Jeff Somogyi comes from partner site Dealnews.

Confused by all the abbreviations and categorical information that accompanies a diamond? Need a way to get your bearings on the wild seas of gemology? Below, we’ve collected together everything you’ll need to know to decipher diamond ratings – which gives you more time to think about what style of ring will be perfect for the girl of your dreams.

As everyone will tell you, you’re going to have to watch out for the “Four C’s”: Cut, Color, Clarity, and Carat weight. What everyone doesn’t tell you is how to look out for them, so let’s investigate what each one of these things means. Of the four, one has absolutely no quantitative scale at all (but is simply the buyer’s preference); two have handy scales – determined by the Gemological Institute of America (GIA) – that you can refer to; and the fourth is so simple to understand that we almost don’t want to insult your intelligence by discussing it. (But we will because thoroughness is next to godliness.)


Most jewelry store diamonds are cut as a Round Brilliant shape, which is, not surprisingly, the most commonly envisioned shape of a real diamond. (Your deck of playing cards doesn’t count!) The Round Cut diamond shape and proportions are nearly consistent across the board, no matter who has cut it, so there’s very little deviation in the looks of most Round Cut diamonds. This cut is shaped in such a way that refracts and reflects all light up through the top of the stone, resulting in its sparkly-ness (which should be an official term and measure for a diamond, but is sadly not). Your Gemologist depicts light refraction and reflection here.

If a jeweler doesn’t follow a specific, mathematical procedure in his cutting of the gem, he’ll end up with a stone that looks like a diamond, but doesn’t have that certain “sparkle” that a diamond should have. To ensure you get a quality Round Cut diamond, the gem should come with an American Gem Society Diamond Grading Certificate.

Even though Round Cut diamonds are the most common, there are other cuts to choose from too. And, whereas a different cut doesn’t necessarily mean the gem won’t impress the lady, Round Cut is by far the most popular. Other common cuts are the Baguette Cut and Princess Cut. Baguette Cut diamonds show off the rock’s luster, whiteness, and clarity, but don’t sparkle as much, and accordingly have less “fire” (color and white light refraction). Princess Cuts, however, accentuate the fire and brilliance, but are not as lustrous.

In what might be an apocryphal story, the jeweler who helped me pick out an engagement ring said, “Don’t go with Princess Cut unless you’re sure she likes Princess Cut!” Take that as you will.


Clear diamonds, or Type I, are scaled by letter from least impure to most impure. According to the GIA color grading scale (the most common scale used), the “purest” Colorless stones are graded from D to F, “less pure” Near Colorless diamonds from G to J, and Faint Yellows are graded K to M, Very Light Yellows are N to R, and Light Yellows are S to Z.

So, a grade D is “OOOOH! So clear! So sparkly!” and a grade Z is “Yellow is your favorite color, right?”

Type II diamonds are of the colored diamond set and can be described as Pink, Red, or Blue. These are a more rare type of diamond – as only 1.8 percent of all diamonds mined are of this type – thus, they are more expensive. There is no scale for grading this subset, however.


Clarity is determined by the number and severity of inclusions and blemishes within or on the cut stone. “Inclusions” refers to anything within the diamond that affects its luster or brilliance, such as cavities, clouds, or other internal flaws. Blemishes, on the other hand, are external defects that affect the sparkle of the gem. Polish lines, scratches, nicks, pits, and chips are all classified as blemishes.

Once again, the GIA jumps in with a handy scale for judging clarity, though this one is not as direct as for color. Balancing inclusions and exclusions, the grades from best to least-best are as follows: Flawless gems receive an “FL” grade; Internally Flawless are called “IF”; Very Very Slightly Included diamonds are deemed “VVS1” and “VVS”; Very Slightly Included receive “VS1” and “VS2” grades; Slightly Included diamonds are “SI1” and “SI2”; and Included cut diamonds are deemed “I1,” “I2,” and “I3.”

It’s likely that the only diamonds you’ll notice flaws in with the naked eye are in the I1, I2, and I3 “Included” category, but all diamonds do have flaws. The trained eye with the aid of 10x magnification can spot these.

So, let’s recap: An FL diamond is, “Eek-gads, my eyes can’t handle the beauty!” whereas I3 diamonds are, “I think you need to clean your diamond.” Will you or the recipient be able to tell the difference between an FL and IF diamond? Probably not. And since the savings can be significant by choosing “down” the scale, it’s a possible way to get a great-looking diamond at a slightly lower price.

Carat Weight

This is the easiest of the four “C’s” to understand. In brief, the higher the carat weight, the bigger the diamond. Boom. Done. We told you one of these was so simple we felt bad even defining it!

Of course, the bigger the diamond, the bigger the price. But, interestingly, since bigger diamonds are harder to find than smaller ones, there isn’t a 1:1 direct size-to-price scale: As carat weight increases, the price of the stone jumps considerably. For example, a 1-carat diamond will cost more than twice the price of a 1/2-carat diamond. (You can’t just meld two 1/2-carat diamonds together!) Keep that in mind when doing your budgeting for the rock.

That handles those pesky “Four C’s,” but there are a few other bits of nomenclature that you might run into when buying the “big sparkly.” Among them are:

TCW (Total Carat Weight)

Many merchants will list a TCW number on items that have more than one diamond or gem. This label is especially tricky when purchasing earrings. Why? Well, if a merchant says that a pair of diamond earrings has “1/2 TCW,” what they are really saying is that each earring has just a 1/4-carat stone. But, of course, merchants know that you’d rather have 1/2-carat diamonds, so they add the total weight up and advertise it like that.

K (Karat)

Differing from the Carat Weight of the diamond, K (karat) refers to the setting in which the diamond has been placed. This measure tells you the purity of gold or platinum in the metal setting. For instance, if you’re considering a Diamond 18K White Gold Ring, that 18K is not referring to the weight of the diamond, but the type of gold used in the band. Pure gold (and, thus, the most sought-after and expensive) is graded as 24 karat (K) and the scale slides down from there. 18K Gold is only 75 percent gold and includes 25 percent impurities by mass.

CZ (Cubic Zirconium)

A diamond imposter. These gemstones are often presented as pseudo-diamonds because they mimic many of the diamond’s attributes. However, their color and clarity are what sets them apart: CZs are synthetic, flawless, pure white stones (Grade AAAAA), and when hit with light only refract a rainbow of colors (all fire, no brilliance).

You should now be armed with the knowledge you need to confidently spend two months’ salary on a diamond. (Bonus tip: That “rule of thumb” is said to have been created by De Beers to sell more diamonds!) But, no matter what you decide to spend, just make sure she’ll say yes!

Check out the latest jewelry deals and put your newfound diamond knowledge to the test.

Stacy Johnson

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