Hi all - just about to go home, so have to be quick & unproofread..

I was convinced I was contralto - but in fact I'm mezzo-soprano.
Alice's excellent posts are what convinced me to try a singing teacher - and I was lucky to find a really fantastic teacher who has made a phenomenal difference to my voice in a couple of years worth of lessons.
I had always sung very loud & very low - which meant that I had a disproportionately developed chest-voice, and only really knew how to belt it out. I still like singing in that low range (especially for blues) - but the operatic singing in my real range is like flying. And the benefits of learning operatic techniques spill over into my other styles - eg a bit of subtlety for a change....
My teacher took a while to decide whether I was soprano or mezzo, and I understand that a big indicator is where the "breaks" occur. I should point out that the voice moves around a bit, and the breaks move too - hence the confusion. It is quite strange when your voice "moves" and suddenly the quality notes are in a slightly different place. Sometimes disconcerting when you suddenly have a problem with notes you used to sing fine - messes up the repertoire a bit! I'm told that you can lose a bit of range temporarily whilst learning - but it does come back - so you have nothing to lose.
Another weird effect is that as the good quality notes spread, it can make the rest of the voice sound really crap! much like painting one room in your house makes the rest look shoddy. All evens out in the end though.
Sorry - am rambling & threadcreeping a bit - also evangelising about getting a proper teacher .........
As to true contralto - no idea why rare - will ask my teacher for an opinion next week. However - definitely I agree with Alice's suggestion that alto's can be untrained mezzos - I was....

Cheers

Kris