I have to agree with these guys...it really depends on your relationship. I, like Yekim, am fairly recently engaged. My SO would've been happy with a chip of glass in a tin foil band, but being the idiot I am, I just can't buy something cheap, especially under the pretense that it is the one-and-only, once in a lifetime, super special purchase, so I ende d up spending a hell of a lot more than I could reasonably afford. It made her happy, though, so that's what counts! Anyway, did the jeweler happen to grade the clarity of the diamond for you, as well as the color? Those are much more important measures than the weight or size of it. A .56 diamond could look like a little ugly glass chip if it lacks clarity and is yellow in color. Or, it can look enormous if it is of good quality. The only way to judge color is by comparing it to a master set of diamonds, but you can get a rough idea of the clarity by looking very closely at the diamond in good light. If you can see any surface blemishes or inclusions (little black things inside the diamond) then it is not better than "I" clarity. The next grade up is "SI", meaning "slightly included", which has inclusions that are invisible to the naked eye, but can be seen with a 10x jeweler's loupe. Price between clarity grades is an enormous jump. For example, I ended up paying more for an 80 point (100 points equals one carat, so 80 points is slightly over 3/4 carat) diamond with SI clarity, but it looks like an easy carat when you look at it. So, anyway, it may be worth it to get a full appraisal and see exactly what you have, as well as an inspection for chips and stuff. If it is a really good diamond, and you have thoughts of tying the knot somewhere in the near future, then I would suggest holding onto it for that purpose. It's not everyday that someone just finds a diamond, and it may be a sign from wherever! OTOH, women see it as bad luck to wear a diamond that has been worn before, so it might actually backfire on you. Just depends on your woman! If thoughts of marriage are few and far between, then think about selling it, buying some nice knives, and getting a little something for your old lady, too! The possibilites are endless! If it is a really good diamond, though, it would be well worth it to hold onto it. When you start shopping for rings in stores you'll be VERY, VERY glad you did! Good luck!
Steve