How do you know they have ?agate crystals? inside? I have never seen
one....Agate forms in massively with layers of various materials
(fortifications)....not as crystals. Agate can form as spheres
(geodes), in layers or in amorfous chunks. If there are crystals
present, they would probably be quartz ( including amethyst,
citrine, etc) with possibly other minerals (eg., calcite) thrown in.
Second, how can you know there are crystals inside, of whatever
category? Some people can tell by the heft (approx weight per mass)
but even that is not always a sure thing.
Actually, all the above is secondary to what blade to use. Agate and
any quartz crystals therein are all a 7 in Mohs hardness (or
thereabouts depending on what other impurities might be present). If
the stone is large, I would recommend using either an MK guillotine
or gemking segmented diamond blade. The guillotine is more for
hobbiests and is a bit cheaper than the gemking which has higher
concentration of diamond on the rim and is more expensive (these two
blades in 6" size run from just over $50 to over $60). If the stone
is smaller, you could get away with either an MK -303 or Dia-Laser
continuous rim blade (prices from $30 to $40).
One thought, don't try to cut a large rock with a small saw.
Remember, a 6" saw blade only shows about 2.5" of blade above the
table. You should not cut a stone over 2" in depth on such a blade
as it could overload the blade and motor.
If the stone is larger than you have the saw to cut, I suggest you
contact a local gem and mineral club...many of them have saws
available. Our club in SOFL has a number of saws from 24" to 4" and
we cut for members for a reasonable fee.
Cutting agate geodes can be really exciting because there is always
some mystery to what you will find and, because it will be the first
time human eyes will see what has been hidden away for thousands of
Good luck with your cutting and I hope you find a real treasure!!
Cheers from Don at The Charles Belle Studio in SOFL where simple
elegance IS fine jewelry! @coralnut2