Nephrite and Asbestos
Nephrite is not asbestos. The confusion arises from the fact that nephrite has the same chemical composition as one of the forms of asbestos (Actinolite).
The characteristic of asbestos that causes 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. The real problem with asbestos is the quantity of fibers that are released when the material breaks up. The fibers are not tightly bound together and break up easily when they are disturbed. With nephrite or chalcedony the fibers that are released are just what you grind out.
So there is no problem with nephrite, right? No, there is a potential problem. Sanding any silicate can generate silica particles and silica, when freshly ground, is suspected to be even 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 micron 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 the time one is exposed to them determine the level of expected toxicity. In either wet or dry sanding one is being presented with the possibility of exposure. If one is worried about it, and anybody doing this probably should be (especially a smoker)—wear a good respirator, and wet-mop the lapiday area frequently. Remember, the largest source of silica most of us are exposed to every day is house dust. Here are some selected excerpts from a series of reports available on the internet on asbestosis and silicosis.
As far as I know all silica is subject to the formation of a hydroxyl layer in the presence of moisture. The removal of this layer is supposed to be how it polishes. This layer is softer than the silica underneath and would be removed in time by friction. The speed with which this occurs would be a function of the physical structure, I would assume, but in any case there is speculation that freshly cut fibers would be sharper and therefore worse on the lungs than fibers that have been around for a long time. If true, it would reduce the danger from house dust a little. As far as the time they stay around, it should be the same. The settling time is mostly a function of the particle size. When the particles get down to the 5 to 15 um range (where the worst damage is believed to occur) they are not visible to the eye and stay airborne for a long time.
When one reads the literature on asbestos it becomes apparent that even the “experts” don’t agree on all of the details of the situation. They don’t all agree which is worse, asbestos or silica, and how fast the problems occur. But most agree that smoking makes the situation worse quickly. I would suggest that every smoker should definitely wear a respirator while cutting and polishing stones, and that even non-smokers should seriously consider it. 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 the public library; even if they don’t have the information they may be able to get it. For some of the more technical reports one 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, so as to be able to make informed decisions about the level of risk we are willing to accept.
For more information on safety issues for artists and craftspersons, read Michael McCann’s excellent book, Artist Beware, reviewed on this site.
Chemical Composition
“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, available online, 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.
“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.”
Asbestiform Fibers: Nonoccupational Health Risks, Committee on Nonoccupational Health Risks of Asbestiform Fibers, Board on Toxicology and Environmental Health Hazards, Commission on Life Sciences, National Research Council, (1984).