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
@doug