LAPIDARY DIGEST
Administered by Hale Sweeny (hale2@mindspring.com)
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This list digest contains the following message subjects:

1. LapDigest News for Issue No. 162 - Wed 8/5/98
2. NEW: Nephrite vs Asbestos
3. NEW: Filling Pits in Cabs
4. NEW: Core Drills for Making Sphere Preforms
5. NEW: Cerium- Color vs Purity
6. NEW: Mixing Saw Oils
7. RE: Tumble Finishing Cabs
8. RE: About Charoite - Mineral Properties
9. RE: About Charoite - Grades of Lapidary Material
10. FS: Bay of Fundy Agate


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<MSG1>

Subject: LapDigest News for Issue No. 162 - Wed 8/5/98

I am pleased to include the article, below, by Dick Friesen
on the reported dangers of dry cutting jade. And you might
want to GET the other file, named DangersOfRockDust.txt, from
the Archives and read or reread that one.

There are several single theme issues which are in the works,
and these include: Polishing, Honduran opal, and Intarsia. I
would like to have issues on use of seashells (e.g.:abalone)
in lapidary, on flintknapping and on condor agate. Would also
like to have an issue on scrimshaw, and another on lathe
turning of lapidary objects, but I have not yet found anyone
willing to write these for me. If you do any of these and are
willing to contribute, please let me know.

Now for a personal request. As described below, we have a
chance to buy 60 pounds of charoite at $8/pound plus freight,
but I only want 10 pounds. Anyone else want to go in with me,
with about a 10# minimum each?

Stay safe, gang!!

hale
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<MSG2>

Subject: NEW: Nephrite vs Asbestos

<<I hope you're not one of those who cut and polish their
rock in their home or garage. Jade "Nephrite" is Asbestos.
Please don't DRY CUT Jade, or advise others that they
should.>>

There are several excellent articles in the archives on the
hazards of dry grinding and sanding and it is probably a good
idea for all of us to re-read them from time to time. But it
helps to keep the problems straight. Nephrite is NOT asbestos.
The confusion arises from the fact that nephrite IS the same
chemical composition as one of the forms of asbestos
(Actinolite). The characteristic of asbestos that cause
trouble is its ability to easily break into fine fibers that
are too small to be seen by the human eye. Nephrite does not
have this character. Nephrite is a amphibole silicate but
physically it is similar to chalcedony in that they both have
a fibrous structure. Nephrite fibers have different
directional hardness which results in its tendency to orange
peel.

So there is no problem with nephrite, right? No, there is a
potential problem. Sanding any silicate can generate silica
particles and silica is suspected to be slightly more toxic
than asbestos. Wet grinding controls the heavier particles
and is definitely recommended on material that does have a
chemical toxicity as well as being a good idea anytime.
Sanding (wet or dry) can produce particles in the 5 to 15 um
range, the size which is suspected to cause the worst lung
damage. In wet sanding, the particles can, and do, get carried
away from the sander as a fine mist. This mist is fine enough
to stay airborne for some distance and the potential for
inhalation is there.

With the fine sanding I am recommending for nephrite, most of
the material is held by the sanding belt and the "jade on
jade" burnishing action actually removes very little material.
But there are still some nephrite particles floating around
and the potential is there for inhalation.

Polishing also produces airborne particles, but I have not
been able to find any reports on the carcinogenic effects of
the oxides we use, so I guess we are safe there for a while.
But even this may not be correct. I have heard that chrome
oxide may be toxic, but I have not been able to find the data.

With either asbestosis or silicosis the number of particles
per cubic centimeter, their size, and exposure time is the
measure of the level of toxicity being presented. In either
wet or dry sanding you are being presented with the
possibility of exposure. If you are worried about it, and you
probably should be especially if you are a smoker, wear a
good respirator. But remember the largest source of silica
fibers most of us are exposed to, all day, every day, is
house dust.

Here are some selected excerpts from a series of reports
available on the internet on asbestosis and silicosis.

-----------------

The term ASBESTOS is a commercial-industrial term rather than
a mineralogical term. It refers to well-developed and hairlike
long fibered varieties of certain minerals that satisfy
particular industrial needs. Table 2-1 lists the names and
chemical formulas of the minerals included in the term
asbestos. Other minerals used in industry, such as
palygorskite, may also crystallize as well-developed, thin
hairlike fibers (i.e., in the asbestiform habit), but they
are not called asbestos.


TABLE 2-1. Mineralogy of Commercial Asbestos
------------------------------------------------------------
Commercial Mineral Mineral Chemical
Name Name Group Formula
------------- -------------- ---------- -------------------
Chrysotile Chrysotile Serpentine (Mg,Fe)6(OH)8Si4010

Crocidolite Riebeckite Amphibole Na2(fe3+)2(fe2+)3
(OH)2Si8022

Anthophyllite Anthophyllite Amphibole (Mg,Fe)7(OH)2Si8022

Amosite Cummingtonite- Amphibole Mg7(OH)2Si8022
gruneritea Fe7(OH)2Si8022

(No common Actinolite- Amphibole Ca2Fe5(OH)2Si8022
commercial tremolite Ca2Mg5(OH)2Si8022
name;sometimes
called amosite)


Chemical Composition

The possible significance of certain elements contained in the
chemical formulas of fibers in relation to disease is under
study. In initial investigations of the health effects of
asbestos, the chemical composition of the fibers was expected
to be important. The most obvious candidate for the common
chemical component was silicon, since all commercial forms of
asbestos are silicates. The likelihood that silicon plays a
role in carcinogenesis is minimized, however, by the
exceptionally strong and almost indestructible bonding of
silicon to oxygen in a tetrahedral structure. Furthermore,
neither other silicates nor pure silica particles have
carcinogenic properties similar to those of the asbestiform
fibers.

Magnesium was next considered, since it is present in most
asbestos and on the chrysotile surface. However, it was soon
recognized that one of the major types of asbestos
(asbestiform grunerite) contained relatively little magnesium
and that another type (crocidolite) did not necessarily
contain any magnesium in its chemical formula.

The most serious health effects associated with exposure to
asbestos are lung cancer, mesothelioma (an almost invariably
fatal form of cancer), and asbestosis (a noncancerous but
debilitating and sometimes fatal disease). In addition, other
nonmalignant lung changes have been documented.

Our review then examines the carcinogenic potency of glass
fibers to humans in comparison with asbestos fibers and
concludes that on a fiber-per-fiber basis, glass fibers may
be as potent or even more potent than asbestos.

Silicon carbide whiskers have the potential, at least, to
cause significant immediate and long-term pulmonary damage.
It appears to be more toxic than crocidolite.

-----------------

On any health related matter please don't just take anyone's
word, including mine, on the subject, look it up. The
internet is a good place to start but remember not all
internet information is created equal. Check on who is
presenting the information and check out their sources. Go to
your public library, even if they don't have the information
they may be able to get it. For some of the more technical
reports you may have to go to a University library.

Unfortunately, there are real hazards associated with almost
everything we do, the problem is trying to get correct
information to be able to make informed decisions about what
level of risk we are willing to accept.

Dick Friesen
friesenr@ix.netcom.com

non commercial republish permission granted
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<MSG3>

Subject: NEW: Filling Pits in Cabs


Hello,

I have accumulated a number of nice cabs that have some minor
pitting on the surface. I have tried filling the pits with
both Opticon and 330 Epoxy between the 600 and 1200 grit
sanding stage (Nova wheels). The problem is that the epoxy
will undercut every time.

Also tried applying the epoxy between 1200 and 14,000 but the
14,000 wheel will not cut the epoxy at all. I am wondering
if anyone has successfully dealt with this problem because I
would hate to trash otherwise beautiful cabs on account of a
few pits.

Any assistance on this matter would be greatly appreciated.

Thanks,
Derek Morton
DMorton567@aol.com

*non-commercial reprint permission granted*
-------------------------------------------------------------
(Note: You may wish to GET the file FillingFlaws.txt from the
Archives, as it touches on this problem. hale)
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<MSG4>

Subject: NEW: Core Drills for Making Sphere Preforms


Hi Sphere makers,

Do any of you use large core drills to cut your sphere blanks
from rough material?

I've got a 70 lb. boulder of rainbow obsidian, that would make
about a 7" diameter sphere, and since we don't have a slab saw
that big, I'd like to find a reasonably priced core drill that
size (commercial ones are running around $500).

I've heard rumors around Quartzsite, that there is a man who
custom makes core drills by pressing industrial diamonds into
soft copper pipe just for this purpose. Anybody have a name
and number of such a person?

It has also been suggested that I find some 7" diam. copper
pipe, braze a cross bar and drill shank across the top, and
use it in a drill press with loose SiC grit, water, and a
clay dam to slowly drill through this 8" thick boulder. That
I could do, but I'd like to get a sanity check on the idea
before I run out to the machine shop to get something like
this made.

Welcome all comments,

Wayne Moorhead
wmooreh1@san.rr.com
San Diego Mineral & Gem Society
http://www.san.rr.com/sdmg/

"non-commercial republish permission granted"
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<MSG5>

Subject: NEW: Cerium: Color vs Purity

<<When working with cerium oxide check to make sure that
it is white, if it has a pink tint to it it has been
contaminated and won't work right.>>

From: "CERIUM A Guide to its Role in Chemical Technology"
by Barry T. Kilbourn
Published in 1995 by
Molycorp, Inc.

CeO2, when pure, is a very pale yellow probably due to
Ce(IV)-O(-II) charge transfer transitions. The color of the
oxide is sensitive not only to stoichiometry but also to the
presence of other lanthanides. A slight trace (~0.02%) of Pr
results in a buff color attributable to Ce(IV)-Pr(III)
transitions. (With higher values of Pr (~2%) the material
becomes a potential red pigment.[14]) Grossly
non-stoichiometric ceria samples are reported to be blue,
related to Ce(IV)-Ce(III) transitions. In addition, as the
oxide is usually produced by the calcination of a precursor
salt, the observed color depends on the extent of that
calcination.

The most efficient polishing agent, by far, for most glass
compositions (particularly those produced commercially in
large volume) is cerium oxide. This application consumes,
either as a moderately pure oxide or as a cerium-oxide-
dominated concentrate, a significant portion of the cerium
products produced annually. Commercial glass polishes are
based on cerium oxide powders with defined particle sizes
and controlled dispersibility in aqueous systems.

The cerium concentrate (predominantly cerium oxide), derived
from bastnasite, is an excellent polish base. In addition the
oxide derived directly from the natural ratio "rare-earth"
chloride, as long as the cerium oxide content is near, or
above, 50 %, provides an adequate glass polish; the
polishing activity is better than the CeO2/LnO ratio would
suggest. Materials, prepared prior to any lanthanide
purification steps, are the source for the lowest cost
polishes available that are used to treat TV face plates,
mirrors and the like. For precision optical polishing the
higher purity materials, based on separated cerium oxides,
are preferred.
------------------------

In other words, the color of cerium oxide is a function of
trace lanthanides and which polishing process it is being
manufactured for, not that it is contaminated. I would
suspect that if it is pure white, and works well, it may be
mixed with aluminum oxide. I have never tried mixing the two,
but I have used tin oxide mixed with Linde A and that gave
good results. Someday when I have some extra time I'll give
it a try and let you know the results.

Dick Friesen
friesenr@ix.netcom.com

non commercial republish permission granted
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<MSG6>

Subject: NEW: Mixing Saw Oils

What are opinions on mixing saw oils? When I bought my (used)
12" slab saw, I drained and kept what ever oil was in it,
cleaned the reservoir and refilled with fresh Almag. I kept
the original oil and after settling, carefully poured it off
into a bucket which has been sitting in my garage. I'm trying
to decide what to do with it. It's a light oil that smells
like it is petroleum based (but definitely not kerosene). It
is light brown, but that might be a result of its previous
use.

Art Berggreen
art@acc.com
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<MSG7>

Subject: RE: Tumble Finishing Cabs

<<The stones go into a Vibrasonic tumbler (manufacturer
doesn't matter) with 600 grit and only enough water to
allow the grit to cling to the stones. This is important!
Most people use too much water.>>

I've heard this before, but I've never been told *why* it's
important not to use too much water? What happens if you do
"overwater"?

Tom

Tom's Gems -- Facet, Cabbing, & Carving Rough
http://www.TomsGemRough.com
FREE PRICE LISTS: Send "subscribe" to Tom@TomsGemRough.com

non-commercial republish permission granted
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<MSG8>

Subject: RE: About Charoite - Mineral Properties

Discovered in the 1970s, Charoite is only found in Russia
at Aldan along the Chary River (for which it was named).

The lapidary material occurs as a rock rather than as the
mineral; canasite, a greenish yellow mineral, may occur with
it in the rock. Other minerals in the rock may be needles of
black aegerine-augite, orange tinkasite and green microchne.
These combine to give a very dramatic effect with colors
ranging from lavender to lilac to purple with contrasting
patterns in orange, green, and black, with swirls of fibrous
chatoyant groups.

Some data about the mineral charoite are:

Chemistry: Calcium potassium silicate. Given in TMD as
(K,Na)5(Ca,Ba,Sr)8Si8O46(OH,F)+nH2O
Class: Silicate
SubClass: Inosilicate
Color: White, lavender, lilac, violet and/or purple
(In Russian, called the 'lilac stone')
Transparency: Transparent to translucent
Luster: Vitreous to Pearly
Streak: Pale purple
Hardness: 5 - 6
Sp. Gravity: 2.5 - 2.8
Crystal System: Monoclinic
Habit: Massive fibrous interlocking crystals
Fracture: Conchoidal
Cleavages: 3 (in three directions)

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<MSG9>

Subject: RE: About Charoite - Grades of Lapidary Material

According to Bridget Easley [1] of White Nights Co. up in
Alaska, there are several grades of charoite. Bridget has
been importing minerals from Russia for several years, and
she has been selling AAA, AA, A and B grades. I asked her to
define these grades for us, and she said:

"The main difference in the charoite grades is percentage of
inclusions. AAA will have none; just bright, bright purple
with silvery chatoyant strands. In my career, I have seen
maybe 20 pounds of it; total. The best way to obtain this
material is to cut it out of the lower, included grades, or
get it already in a Russian-manufactured form (I have
Russian-cut AAA cabs, for example.) The main reason it's so
rare is, well, it falls apart when cut. Probably takes one
pound of material just to get one good cab."

"AA is just as nice, but has up to 10% black augite,
white/green Feldspar, and orange Tinaksite inclusions. "

"A is up to 25% inclusions. B has more inclusions than that,
or the purple has grayed out some. If it gets too included,
gray, or brown; it's just not sold."

"Grade is according to rarity, but is in inverse proportion
to ease of cutting. The lower grades are far easier to cut;
the material holds together better. I always recommend that
beginning cutters start with that. In addition, except for
fine specimen collectors, most people prefer the included
"matrix" appearance of the A grade. Just looks more
interesting."

She tells me that she is closing out charoite in general and
has 60 pounds of A and B grade chunks which she will offer
for $8/pound. Anyone interested may contact her at
<bridget@Alaska.net>.

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<MSG10>

Subject: FS - Bay of Fundy Agate


Would any cutters/collectors/dealers on the list be interested
in a lesser known but sometimes downright spectacular Bay of
Fundy agate? It's mentioned as being "fine quality" in John
Sinkankas' "Gemstones of North America?"

The agate in question is Two-Islands moss and plume agate,
from Two Islands near Parrsboro Nova Scotia on the Bay of
Fundy. These islands in fact were acquired by a jewellery
manufacturing company just before the turn of the century as
a potential source of gem rough. As far as I understand it,
the material is no longer available to collectors, the area
being now under a commercial mineral claim. One piece I saw
last summer, just a bit smaller than two ordinary red
building bricks laid side by side, say about 8 pounds in
weight, sold for $120 Canadian ($80 US) at the "Rockhound
Roundup" in Parrsboro.

I have somewhere around 60 to 70 lbs of this material,
collected some years back. The basic theme is red and orange
flames on a clear to yellow to brown background; also some
smaller pieces of "porcelain agate" from fist-size on down.
It's a little hard to describe in words just how attractive
this material is, so if you're interested, e-mail me off list
and I'll gladly send you a few jpegs.

Cheers,
Hans Durstling
sinico@nbnet.nb.ca
Moncton, Canada
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