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Lapidary Question: Ruby in Zoisite

I’m trying to polish a nice ruby in zoisite cab. It stone looks
crystalized or “sugary” even though it is VERY hard (especially the
ruby portion). Can’t seem to even get it to a high luster. Any
ideas? Thanks a bunch.

Cathy Flory

assuming your issue is with the ruby part, not the zoisite part.
Most of the ruby in zoisite suffers from 2 problems; a) high amount
of internal cracks, and b) grain orientation.

Polishing with the grain works, I recommend 600, 1200, 3000, 8000
and 14,000 diamond sequence. 50,000 and 100,000 if you are fussy.

Subsurface breakage, only way to solve this is by sawing a piece,
and use portions from the inner 80% of the stone, avoiding those
that are within a distance equal to 10% of the diameter of the stone
(i.e., 5" piece, stay away from out 1/2 inch).

hope that helps
Mark Zirinsky
"private cutter buying rough and collections"

Hi Cathy,

The challenge with this material --in fact,any rock comprised of
minerals of dissimilar hardness, for that matter – is that the
matrix tends to undercut at about the same rate that the harder
material(s) polish. Your best bet is going to be using plated or
sintered steel-and-Diamond wheels with a copious water flow, and
taking your time. Despitewhat may be aninnate desire to get the
stone over and done with, already, I think you’ll find you’ll do
much better if you go back toyour 600 and 1,200 mesh steel wheels,
followed by 3,000 and 14,000 wet Diamond belts, and finish with
50,000 mesh compound on either a pellon or synthetic canvas belt or
disc. The trick with Chrome Zoisite seems to be to focus on the
matrix, not the Rubies; if you cut and polish radially – that is,
start cutting or polishingfrom the matrix, and work in towards the
center of each Ruby crystal, you’ll be less apt to develop those
separations where the two meet. Also, be sure to use a much gentler
touch than you would with most other materials. Treat the Zoisite as
if it were some of the chalkier Turquoise from the old Kingman Mine
and you were trying tokeep the brown matrix from washing away; the
feel and technique are similar. Last, but not least, try to keep in
mind that the massive Zoisites – both this and Thulite --are
essentially “sandstones” made up of a mineral whose individual
grains, in and of themselves, have different hardnesses depending
upon their direction. So, what may behappening is that you’re
treating the whole as a solid, rather than a composite. Just as I
teach students to consider the hardnesses and characteristics of the
inclusions rather than the matrix, when faceting Peridot, I
suggest that you approach this material as a "glued together"
melange of saoft stones with a few hard zones: if you treat it as
it’s softest component needs to be treated, the harder ones’ll come
along for the ride. Hopingthiswill proveuseful to you,

Best regards,

Douglas Turet, G.J.
Lapidary Artist & Designer
Turet Design
P.O. Box 242
Avon, MA 02322-0242
Tel. (508) 586-5690

I posted a few days ago about a problem I was having polishing a
ruby/zoisite cab. I received a lot of good advice, thank you to all
who answered! However, although I tried different methods, I did not
achieve anything close to a polish on this cab until I used a new
polish I just received called “HOLY COW!” polish. Finally, I was able
to achieve a glass polish on the zoisite (which was the difficult
part of the two minerals). This was without much effort on my part. I
am simply amazed at how well the zoisite polished after all of my
failed attempts. Now the Holy Cow won’t polish the ruby, it is too
hard; but that I can achieve with diamond slurry. I just wanted every
one to know about this polish; I plan to go back to some other cabs I
have already finished and use the Holy Cow on it. Disclaimer: This is
not an advertisement for Holy Cow polish, I’m just one happy

Cathy Flory

Cathy, Tha “Holy Cow” polish sounds great, so where can we get some?
Jerry in Kodiak