stone for a green man

[Norman Watts <Norman_Watts@zzzzzzz>]

I want to make a green man, but I want to add quite a bit of detail,
with undercutting and quite fine featured. In fact, I want the foliage
aspect to predominate over the human features by quite a bit. Think of
it more as foliage in which one can discern a face rather than a face
surrounded by leaves. I am thinking of doing it in something like green
marble  -to go with the green man theme. I plan to use a Foredom flex
shaft tool. Can anyone recommend an appropriate type of stone
(strength, carve ability, colour, not likely to contain major flaws)
and maybe a good source for this stone. I'm thinking about human head
size.