Cutting agate

I recently aquired a couple of round stones that have agate crystals
inside but have not been cut open yet, I was wondering what kind of
blade would be best for my stone cutting saw, i know there are
different type of diamond blades but I am not sure what one would be
best, thanks



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

Hi Marian,

I’m assuming that what you have are geodes and you wish to saw them
in half.

Agate (cryptocrystalline quartz) is exceptionally tough on saw
blades. Small blades in the 4-6" range are easily ruined cutting
agate, but if you go VERY slowly, and use oil or a water soluble oil
as coolant, you should be fine. The saw should be running at full
speed, wear eye protection, NEVER stand in front of the blade
itself. Watch where the blade is cutting very closely; if you see
sparks, you are moving too quickly. Don’t try to use too thin a
blade, as it is easily damaged on geodes and the wear will be
excessive. A good sintered blade is best, and, in blades as in most
other things, you get what you pay for. Diamond blades GRIND their
way through stone, you need to go much slower than you think if you
want th blade to last. A two-inch geode, hollow, should take almost
ten minutes. You CAN cut it faster, but your blade will not last
very long.

By the way, a 2 inch diameter geode is too big for a 5 inch saw, if
that’s what you are using.

Wayne Emery
The Gemcutter


Try these sites

I have 2 blades I really like, a Barranca BD 303 in .025 kerf and the
Ukam in .032 were I to pick a favorite, it would probably be the Ukam.

The Barranca I use with oil lube, it was the recommendation of the
store I bought it at.

On the Ukam, they recommended a water based lubricant and a light
feed. They have a lot of on their site that is well worth
the time reading.

Depending on the size of your saw, both of the above would provide
very good service for the rock you plan on opening. If you have a
larger saw, like a 10 to 14 inch and do boulders :slight_smile: I am trying the
Harbor Freight blade, specifically the 10" Tile saw blade, it has a
much faster turning speed than normal ( like 3 times), be prepared to
force feed lubricant to it at its full rated speed and use a light
feed rate of 2 to 3 pounds. I have only had it in service since
November so I am not sure how well it will last yet, but at the price
it was worth the try and so far the cutting has gone very well on
some pretty hard material.

The only blades I have found that I am totally dissatisfied with no
matter the manufacturer, lubricant or feed rate are the blades with
the little steps around the rim.