Consonants and sonorants as vowels

I've been far from my computer for a while and I'm happy to find it back.
Fortunately, my girlfriend checked my mail twice a week : all those messages
from the list would have crashed my provider's server ;). So, I must confess I
have not yet read it all.

Well, I was wondering about strange vowels we can find in some natural languages,
such as sonorants (e.g. /r, l, m, n.../) and above all consonants : I've heard
of (african) languages which use sounds like /s, z/ as vowels. I was taught
that sounds can become vocalic with respect to the sonority scale. I don't know
if some natural languages use (voiceless) plosives. Do some of you use such
sounds? Which kind? I'm really interested in that point, and I'm sorry if it's
already been asked.

Bye.

Julien

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