There are several great books on carving. Tom harmon, henry hunt,
work with montana agates.
Myself, I carve jade and agates, have just started a 550 gram smokey
quartz, 7 inches long, the piece is facet grade, and I did not want
to do a large conventional faceted stone
the best way to learn to carve - take a scrap piece of material,
similar to the actual stone you want to finish, and have at it, play
with it, work it, see what you can make it do.
as you grind, work symmetrically, avoid large pits. I recommend
diamond points from Lasco, they will fit your flex shaft. also, use
1200 and 14,000 diamond paste on a hard pad for polishing, avoid
heat buildup on agate or it will fracture.
keep in mind: you know those fantastic oriental carvings from
1700-1920p ad? they were done with wire, sand, and alot of patience.
So, your 6" machine will work well.
Mark Zirinsky, Denver