Diamonds can be an investment, but basically only stones of more than one carat of no grade below C, and then when loose and not in a ring.l Only rings and other jewelery owned by some royal or noble person are worth more than they would be worth loose.
Diamonds are graded A through M. Mostly only a gemologist can actually determine the true grade, and this is almost never revealed by seller. Because of superstition and similar crap, it is rare to give a diamond ring that has not been in the groom's family. So the hapless groom has to fork over three month's wages for the damned thing.
CZ as a rule sparkles more than a diamond costing ten times more.
Symbolically, the diamond serves the same purpose as the Swahili warriors' gift of a herd of cows to the bride's family: to be a successful Swahili, you have to prove that you can raise cattle. The American's diamond proves that the poor bastard has credit, which serves the same purpose in the US.
Of course, the Swahili custom is more practical. You can EAT the damned cattle.
Hocking that diamond ring won't feed anyone for long.
Pretty much everything to do with weddings and funerals are massive ripoffs. Profits that would be unknown to the least honest of used car salesmen are par for the course among jewelers, wedding planners and funeral directors.
Catch this parody on DeBeers' annoying commercials:
http://www.youtube.com/watch?v=OiN-EqwIYJI&NR=1
