im sure that synthetic diamonds are cheaper...they are used in cutting tools or tools to polish diamonds

check this

synthetic diamonds wiki

i couldnt agree more to the points that hawk has brought up
if it wasnt for debeers i think man-made diamonds aka cubic zirconia or lab actual grown diamonds will make it into the market, just like how other natural occuring materials are being substituted with man-made ones

I dont see how is it unromantic to give your wife a man-made diamond.
they look the same, feel the same, last as long, same chemical composition etc.
can an untrained person even tell the difference?definitely not. Lab grown diamonds can even have the same kind of cut that a natural diamond would. I'm sure if your wife loves you she wouldn't mind as it still sparkles like natural ones.

how are man-made diamonds different from natural occuring ones?
they are still carbon with the same crystalline structure so the refraction index will be the same thus cuts that are available for natural ones will be available for man-made ones as well