MOP Health Hazards

Is Mother of Pearl dust dangerous? I had to do a project requiring
the grinding and shaping of M.O.P. In spite of the fact that I wore
a mask, I’ve had a head ache and sinus pressure for two days now.
Any thoughts on this?



Now is a fine time to tell you, but you ‘do not’ grind rock or shell


You have sinusitus. MOP is calcium chloride, otherwise known as
chalk, as are pearls themselves. There are other trace elements - if
you notice, it smells like the ocean when cutting it. It is not
officially considered to be hazardous, except the dust will get
through masks and plug up passageways. I get the same thing cleaning
out old garages and attics, at times. That is to say, dust is not
good for your sinuses, but it is not TOXIC. Abalone shell IS, though,
so you need to look out for that.

MOP is calcium chloride, otherwise known as chalk 

Chalk is calcium carbonate, isn’t it? Neither one is good to
breathe, of course.


Hi Julia,

Yes, Mother of Pearl is dangerous, as are Malachite, Azurite,
Turquoise, Variscite, Chrysoccolla, Chrysoprase, Sugilite, etc., etc.
If you must work with these, then take the necessary precautions:
make sure your shop has adequate ventilation, including both stale
air evacuation and fresh air replacement ventilators (check Charles
Lewton-Brain’s site for some valuable insights, here), that you’re
using an abundant water drip on your workpiece and tools, and be
certain that the mask you’re wearing is of the dual canister
respirator type – not just the flimsy paper masks some jewelers
wear, which have all the stopping power of a fishnet, when it comes
to small, dangerous particulates.

What’s at work here – that is, the chemistry underlying all of this
– is that our blood is “hemo-” (or iron) based, and these materials
are calcium-, copper-, nickel- or manganese-based, so when we get
some of their “stray” molecules into our bloodstreams, we get
anywhere from slightly to dangerously poisoned. (and no, I’m not
exaggerating, when I use that word.) Because our electrolyte systems
can get thrown so far out of whack so easily, it really doesn’t take
much, to leave you with a bad taste in your mouth (literally), so it
pays to make sure your bases are covered, before tackling jobs like
this. (In the future, when you come up against jobs like this, let me
know and I’ll see what I can do to lend you a hand, or phone me, if
you need any help prepping your shop to handle this sort of thing,
firsthand.) I keep one respirator loaded with filter cartridges for
particulates and another for fumes, such as those generated when
doing wax work.

By the way, when you set up your shop’s ventilation system, pay
particularly close attention to how many changes of air per hour your
system will provide you with, and be sure not to remove your
respirator until sufficient time has passed to enable the stale air
and/or gases to exit the room and the replacement air to enter, or
you’ll be back to “square one”, all over again. Last, but not least,
if you have a family doctor, ask him or her whether a medication
called Cholestyramine will be of any benfit to you, now. Once upon a
time, after a similar ingestion situation, it was given to me, as a
means of binding the unwelcome stuff together and flushing it out of
my system. If that won’t work, ask what will, because if you’re
sensitized to this calcium overload – or to the proteins bound to
it --you may not want to mess around with the long-term
after-effects. (I’m not a doctor, and I really don’t know much about
this, save for how uncomfortable I was, when it happened to me, and
how concerned my doctors seemed to be, at the time.)

Hope this’s been of some use to you, Julia!

All the best,
Douglas Turet, G.J.,
Turet Design, LLC
P.O. Box 242
Avon, MA 02322-0242

You have sinusitus. MOP is calcium chloride, otherwise known as
chalk, as are pearls themselves 

Nope. I think you mean calcium carbonate. The make-up of the dust is
not as relevant as the fact that the dust can settle in the lungs
and may have very long term effects, which may, indeed, be fatal
(silicosis). It is wise to use a particulate mask when doing ANY
grinding, even if water is used as a lubricant in the process… The
airborne water droplets contain dust and can get in the lungs as
well. A similar problem exists with the use of oils, both for sawing,
grinding, and faceting or cabbing. While petroleum distillates may
be relatively harmless to breathe (some are very toxic, always
consult the MSDS), the airborne droplets can and do cause a problem
known as pneumonitis. It is an acute (non-persistent) condition
resembling pneumonia in that it exhibits congestion and upper
respiratory irritation.

The persistent inhalation of metal dust and fumes can likewise have
very unpleasant long term results. Use a mask (and don’t forget your
eye protection)!


Since I cut all types of shell I can tell you that many are toxic
especially females of species and some are not that is why I invested
in a good mask that filters those fine dust particles. I would rather
look like darth vader and be safe. (our neighbors in the wharehouse
next door saw me with my mask and goggles on and started doing the
darth vader theme at me and laughing) Hey free longevity to anyone
who sees you via laughs and better still personal longevity.

Silver & Cameo Heritage Jewelry

Mother of pearl (nacre) is mostly calcium carbonate ( so is chalk) it
is not calcium chloride. It contains layers of the carbonate and
layers of a protein It is possible you have an allergy to the protein
in dust formed by working see: and search
mother of pearl allergy You won’t learn much here but look at the two


MOP - Mea Culpa

Someone just asked me the other day if I ever made mistakes writing,
and realized it later… As someone from New Zealand (isn’t the
world a little place!!) pointed out, shells are not made of Calcium
Chloride, but Calcium Carbonate, which is the same thing as chalk.
That’s what happens when you just write on the fly…

Mother of pearl, mussel shell, abalone are toxic regarding dust, and
it should be carved, cut, with a face mask rated for dust, and a lot
of water to keep dust to a mininum. Some years ago there was an
article in I believe, Lapidary Journel regarding the health hazards
of cutting shell. There were some deaths in Mexico, from abalone
shell dust. Please get an appropriate dust mask, and be careful.

Regards, T.H. Gilbert


It has been explained in several posts here that any kind of dust
is harmful. What is the difference between dust created in the
workshop vs. natural dust? For instance, I live in Tucson, in the
desert, with a several year drought, and on a dirt road. There is
so much dust around, that bringing fresh air in from outside
certainly doesn't get rid of dust. It's also my understanding that
natural dust is primarily silica, so what is the difference between
this and silica that is found in a workshop? If I wanted to avoid
all dust, I'd have to be wearing a canister respirator 24/7. 

I am just curious about this. I personally am aware of the dangers
of exposure to toxic substances, my dad has mesothelioma lung cancer
from working with asbestos.

Steven Yaple

Although I have corrected/apologized for mistyping the chemical
formula (chloride/carbonate), I fear that I must speak from
experience, having cut mountains - pounds and pounds -of Mother of
pearl, doing inlay work. When you cut a small quantity of MOP, and
your nose is plugged for several days, you have (in lay terms)
sinusitus, which is a lay term for a plugged nose. Silicosis is a
serious lung desease more related to cancer. Trust me, if you nose is
plugged up from dust, you do not have silicosis. If you’re coughing up
blood, maybe. Let’s not leap off the deep end, huh? Abalone shell is
TOXIC. The word toxic means that is contains Poison. MOP is NOT
toxic. I.E., it does not contain poison. This isn’t made up, it’s what
the word means, in chemical terms. It is an irritant to mucous
membranes, like all dust, and it can cause silicosis in the long
term. You can die, and probably WILL get very ill, if you cut abalone
without ventilation and more, because it IS toxic. Cutting MOP is
identical to cutting chalk, and also marble, and also cured concrete.
Calcium carbonate is common and relatively harmless - Ketchup is
harmful if abused…


A couple corrections may, I think, be in order. First, MOP, like
pearl itself, is made up of more than calcium carbonate. It contains
a protein binder, called conchiolin (spelling?). Not that different
from horn or fingernails. As you say, it’s not usually toxic for
most people. But some few people will indeed react to that protein
material. When that happens, it’s more along the lines of an
allergic reaction than any sort of inherant toxicity, but it can
still be serious. People working with MOP are well advised, at the
least, to work it wet so as to keep the airborne dust levels of both
the calcium carbonate and the protein componant, out of their lungs.

Second, Calcium carbonate does not cause silicosis. Silicosis, as
it’s name suggests, is caused ONLY by Silica in the lungs. And not
just any silica. It needs to be silica flour or particulates of a
particular size, one which the lung’s normal cilia activity does not
remove. The problem tends to be because these particles are sharp
enough to imbed themselves in the lung tissue rather than just
sitting there to be removed like normal dust particles. Calcium
carbonate, on the other hand, simply does not form that type of
aggressive, sharp, splintery particle. The crystals in pearl or MOP
are flat platelets, and grinding the stuff up in working doesn’t
change that. Grind it up smaller than the size of the particles in
MOP originally, and the result is blocky simple shapes, not sharp
shards. Those particles generally are within what the lung can
remove normally. But that depends on exposure levels. Breath in too
much, and any type of particulate can overwhelm the lungs self
cleaning ability, and cause lung damage. Even easier if the person
already has some existing impairment. it can indeed be serious. But
it is not silicosis, a name used to describe the particularly
aggressive damage caused specifically by silica flour particles. I
make the point not to be picky, but because people looking at
symptoms and dangers from silicosis might associate the same danger
level to calcium carbonate dusts from your description, and the two
materials do not present the same risk level. Silica flour is much
more dangerous.


It has been explained in several posts here that any kind of dust
is harmful. What is the difference between dust created in the
workshop vs. natural dust? 

Natural dust is a mix of things, largely silica and feldspars, but
also all sorts of other things, organics, etc. The big difference
between natural dusts and what you “manufacture” in the workshop is
often that what we generate in the shop are particles that are newly
"minted", caused by fracturing larger bits into smaller bits.
Abrasives wear down in this manner, for example. Or quenching
casting flasks fractures the silica particles in the investment.
Either way, the result is sharp jagged shard like particles. Even if
blocky shapes, they’re sharp edged. That makes them highly abrasive
and irritating, and sometimes (silica especially ) able to literally
imbed themselves in lung tissue, so the lung cannot easily clean it
out again. natural dusts, like river rocks, are more worn particles,
less sharp, less aggressive, and easier for the lung to clean away.
The natural stuff is what our lungs evolved to deal with, and
they’re fairly good at it, when the quantity/exposure level isn’t
abnormally high. The stuff we generate in the shop is sometimes much
more dangerous. It depends a lot on just which material is being
turned into dusts…



You can die, and probably WILL get very ill, if you cut abalone
without ventilation and more, because it IS toxic. 

The issue of chloride/carbonate aside, (I did not fault you for the
typo, I knew what you meant). I ran across this;

mother-of-pearl or nacre (nC481’kC999r), the iridescent substance
that forms the lining of the shells of some fresh-water and some
salt-water mollusks. Like the pearl it is a secretion of the mantle,
composed of alternate layers of calcium carbonate and conchiolin.
Among the chief sources are the pearl oyster, found in warm and
tropical seas, chiefly in Asia; freshwater pearl mussels, which live
in many rivers of the United States, Europe, and Asia; and the
abalone of California, Japan, and other Pacific regions.

I do not know which of the above varieties the lady was using who
made the original posting, I had always thought mother of pearl was
Abalone when you got it in the large pieces, seems I was partially
incorrect, but Abalone is one of the sources of MOP.

Thanks for your writing, I would probably not have looked it up…



I am just curious about this. I personally am aware of the dangers
of exposure to toxic substances, my dad has mesothelioma lung
cancer from working with asbestos. 

Unlike asbestos, most of the dust in our lives will leave our body
through our normal mucus processes. Where the problem comes in is the
concentration and persistence with which we are exposed to the dust.
In the shop without ventilation or other precautions we are exposing
ourselves to a greater concentration than would normally occur and
the silica we grind from the rocks or MOP we work with is very, very
fine. In the post you sited, the person talked about living near a
dirt road. Yes you will have a greater concentration of dust, but
unless your genes are prone to it I do not think it will harm you to
any large extent. I grew up on a farm and there were days coming in
from disking this dry ground of Colorado, I looked like a raccoon
where my glasses covered my eyes. My dad had a much greater exposure
than I did as he was at it more than I. Neither of us have had any
adverse effects that we are aware of. My dad is 76 and still working
the farm from dawn to dusk. His doctor is amazed how fast he heals
after the knee and shoulder replacements and he still goes elk
hunting every year. We just don’t make him walk so much any more,
don’t want to wear out his new knees.

The thing to remember is, asbestos is a very nasty fiber which when
it burrows into you, unlike silica which sits on the surface, it does
not come out, it just keeps tearing things up. Very fine silica will
get in the pockets of your lungs and build up but it doesn’t keep
damaging you.

That is how I view the difference between asbestos and silica
dangers. I grind my rocks wet because the sanders produce a very,
very fine powder which is not so easy to get out of you. Remember,
breath through your nose, not your mouth your sinus cavity is a
wonderful cleaner, just don’t overtax it.


It is aggravating to me that people do not distinguish between
things that are highly toxic or dangerous, vs those things that can
have long term health effects with constant exposure. If all dust is
toxic, as some people seem to be asserting, I should be on my way
out as I live in a highly dusty environment.

It has been said that, when a cave man got a shell with a hole in
it, strung it onto some woven grass and put it around his neck, the
world’s oldest profession was born. When he took that shell, gave it
to a woman in exchange for her consideration, then the world’s
second oldest profession was born. When we make a ring, for example,
that ring has never been made before, so it is unique, in terms of
design. The techniques and methods and tools and chemicals that we
used to make that ring are not only not unique, but they have been in
use for thousands of years. We all of us, here on Orchid and
elswhere, are doing nothing that is new. It has all been done before,
again, speaking not of design but the mechanisms of jewelry making.
The Greeks, Romans, Egyptians and yes the Mayans and Incas knew
everything about jewelry (in context: no electricity, etc.) that you
or I know. I point this out not to be negative, but to be positive:
We are part of a tradition, we are a family, we have a heritage. One
of the things that heritage provides to us is that we don’t have to
guess, we don’t have to wonder, and, most importantly, we don’t have
to reinvent the wheel. Since they have bee cutting stones in Idar
Oberstein since the middle ages, all we need to do is look there for
a history of the dangers of dust in lapidary (nil, if done
properly). Then there’s really no reason to get into a panic about
what could be, or might be, or that 6 people developed some disease
last year because they we exposed to something you’ll never see in
your life. Perspective. We have evidence of all things jewelry,
because of our heritage. All one needs to do is realize that, even
though we may be wet behind the ears, fresh out of school, thinking
we are going to somehow revolutionize jewelry and spread the word
about our newfound knowlege, that that newcomer is actually newcomer
#346,589,641 and yes, they get a prize. Then you can get on to
learning from our past. Dust is dust. Save your paranoia for the
important things - cyanide, HF, methylene chloride, nitric acid.

A useful site for air contaminants and respirator is 3M’s online
respirator selection software -

I plugged in Calcium Carbonate at .5mg/cubic meter, with no oils or
hydrocabrons present, and it recommended the standard selection of
the small white disposable N95-rated masks. At 1 mg/cubic meter,
however, it kicked it up to the canister masks.

It didn’t say “no respirator needed,” but then again, I’m guessing
the presumption of the software is that the environment is
dusty/polluted enough to make someone worry that they might need to
select a mask. Safer to always recommend some sort of mask, in other
words, rather than give someone false hope and wind up with a lawsuit

And by the way, the toxicity of abalone shell dust is always widely
reported, but no one ever states just what the toxin is. Something
in the conchiolin? Paralytic shellfish toxin? What? Anybody know for

Staying tuned,

Oh. We’ve been here before! from the Conchologists List:


From - "Dr. David Campbell" 
    I recently read a comment on the chat list of the jewellery
    makers' website,, stating that the abalone shell
    is a deadly one to cut or grind, due to the fact that the body
    absorbs the dust through the lungs or skin. 
Shell dust is calcium carbonate and protein. It's not absorbed
through the skin. Any fine dust is bad to breathe, but there's
nothing worse about shell than average (as opposed to, e.g.,
asbestos). There is a possibility that some treatment of the
shell (polishing, etc.) or something used in the cutting (e.g.,
the lubricant for the saw blade) adds dangerous chemicals to the
mix; such problems could be avoided by getting natural shells and
being careful about saftey with the chemicals you use. 

If the new technique generates very high heat as it cuts, there
is the chance that powder could be changed from calcium carbonate
to calcium oxide. This is a strong base that can irritate the
skin and would not be good for the lungs. However, unless you are
directly inhaling the dust as the shells are cut (as in a large
factory with seriously deficient safety standards), I would not
expect there to be enough to cause a problem. Perhaps more likely
is the possibility that the factory in question had an outbreak
of some serious respitory disease. 

My graduate advisor has been cutting lots of shells for a few
decades. The only health problem he had was cirrhosis due to the
acetone he used in processing the samples. He's been careful
with the acetone since then and hasn't had a problem. 
    The body then interprets this substance as a sugar and sends
    it to all the organs. 
Not likely. The body can recognize proteins, calcium ions, and
carbonate ions just fine. 
    There followed an anecdote about a group of people dying just
    a few months after beginning a new efficient process of cutting
    abalone shell. Pustules in the lungs, death due to pneumonia. 
Large quantities of fine particles (dust) in the lungs is not
good for you, though I suspect you would need closer to a few
decades to have significant problems with shell dust. 
    It was also stated that the dust can be absorbed when
    suspended in a solution. 
If you drink it. 
    I'm going to have to cut some of these shells in my work, and I
    must find a safe way to do it. 
To avoid inhaling lots of dust, assuming that your cutting
methods generate lots of dust, you could get a basic air filter
mask from a hardware store. 

For more you might look into safety for
construction work using marble or limestone (also calcium

Dr. David Campbell
425 Scientific Collections Building
Department of Biological Sciences
Biodiversity and Systematics
University of Alabama, Box 870345
Tuscaloosa AL 35487-0345 USA
but Abalone is one of the sources of MOP. 

Mother-of-pearl is produced from oyster shells. Abalone shells are
referred to as either abalone shell or paua shell, never

James S. Duncan, G.G.
James in SoFL