The other day I heard of a girl who had been given a fake diamond for her engagement and couldn't help but wonder that if she would've known a little about diamonds, maybe she would've spotted the fake right away. There are four C's that define a good diamond and they are: clarity, cut, color, and carat.
Clarity refers to the imperfections and intrusions within a diamond. It is believe that this is the characteristic of diamonds that affects the appearance of a diamond the least, because these imperfections can be microscopic or only visible with a jeweler's lens. Make sure your diamond has no flaws visible to the naked eye as flawless diamonds tend to go up on the price scale.
Carat is the one thing we all hear about but few understand. It refers to the diamonds weight but not necessarily is proportional to its size. The two things to consider when looking at carats is the distance across the top of the diamond in millimeters and the cut grade. The top is important in this because that is the way in which we see diamonds.
Color is easier to identify because it measures that lack of it in a diamond... unless you're getting a blue, red or yellow, then you can be very happy is not colorless! An absolute colorless diamond has a D but those are rare and quite pricey.
Finally, cut is the thing most of us know of because it is the simplest to notice. It is what determines the "sparkle" in the stone and the characteristic that affects the appearance of the diamond the most. The ideal cut is the one that reflects the most light is it does not only on the surface but also from the inside.
Have a great and sparkly day!