why do they call diamonds as women's bestfriend?

i think quite awhile ago when it was important for a woman to be married the diamond symbolized that she was about to get married and ready to have her husband take care of her. such is definitely NOT the case here anymore!

I can't say it's a clue and I'm not a woman either So this is just a pure guess. Maybe because diamonds really looks good when on woman's soft skin. Also diamonds tend to last forever as women tend to always say their love is (?)

actually girls just love diamonds. Thats why they're their best friend. What girl doens't love diamonds?
they're so pretty and shiney o.O lol

i think this is precious stone and if you have bad time you can utilize it by selling ...and any how girls like ornaments and diamond are the best gem for ornament

It's from the song Marilyn Monroe sang in "Gentlemen Prefer Blondes".

If you listen to the lyrics it explains it. It says that men come and go, but diamonds will stay with you forever.

Here:

A kiss on the hand
May be quite continental,
But diamonds are a girl's best friend.

A kiss may be grand
But it won't pay the rental
On your humble flat
Or help you at the automat.

Men grow cold
As girls grow old,
And we all lose our charms in the end.

But square-cut or pear-shaped,
These rocks don't loose their shape.
Diamonds are a girl's best friend.
etc.!