Vermiculite & Asbestos??

by Steve Hill, CO


Vermiculite. Itís that flaky stuff that some technicians use to make plaster casts lighter and cuts down on the amount of plaster required. Iíve never really liked the stuff all that much, myself but I know plenty of folks who swear by it.


But is it a health hazard? In fact, what is it?


I recently saw a feature on the popular TV news/documentary 20/20, about asbestos poisoning in a small mining town in Montana. Workers at a mine, the townís biggest employer, were displaying very high rates of cancer. The cancer was found to be blamed on asbestos, another mineral found alongside the mineral being mined. Additionally, the asbestos poisoning wasnít confined to the mines workers. It had become common in the towns general population.


As it turns out, the asbestos fibers readily cling to clothing and can be transported into the mine workers home. Even if the clothes are cleaned upon entrance into the house, the fibers remain resilient through the washing machine and are imparted to subsequent washes. If you were a miner, your whole family was most likely infected with asbestos fibers, a known cause of cancer.


So what was the mineral being mined in Libby, Montana? Vermiculite.


As I said, 20/20 is a popular TV show and I wasnít the only one who saw that episode. I received a call that week from a technician who was nearly frantic with worry. Heís been using vermiculite for many years and was fearful of having exposed himself to this potentially deadly mineral. He neednít have worried.


Vermiculite, also known by its formal name hydrated laminar magnesium-aluminum-ironsilicate, is a mica-like mineral mined from the earth in open pits. Found in many countries such as China, Australia, South America, Africa and the US, it is a fairly common mineral and has many, many uses.


Itís found in the agricultural industry and is used as an anti-caking material, bulking agent, fertilizer, pesticides and soil conditioner. In construction it finds uses as fire retardant, insulation, an additive to gypsum plaster (like the way we use it) and in sound deadening components. Its uses are wide and varied and can be found in the most unlikely places.


When subjected to heat, vermiculite expands many times its original volume. We typically see an expansion of 8 Ė 12 times but can be as much as 30 times in individual flakes. As the particles expand under heat, they dry out and actually become a little lighter.

So, while they can gain a considerable amount of volume they remain at about the same weight. When added to plaster, vermiculite has the effect of taking up a lot of space and greatly reducing the overall weight of the cast, making it an excellent filler for making positive impressions.


Vermiculite, all by its lonesome, isnít cancerous nor does it contain asbestos. But the report of the Libby, Montana mine didnít make clear how the asbestos came to be in with the vermiculite. As it turns out, the geography of Libby had a somewhat unusual history.


Virtually all of the commercial vermiculite mines in operation today have deposits which were formed in the pre-Cambrian and Archean era (1.5-3 billion hears old). The deposits at Libby, however, were formed much more recently in the Triassic era (225 million years old). The deposit in Libby was originally biotite and diopside. With weatherization over millions of years, the biotite turned into vermiculite and the diopside turned into the asbestos.


So the Libby mine was only contaminated with asbestos which became mixed in with the vermiculite. Vermiculite itself isnít cancerous or dangerous. The mine in Montana could have been a gold or salt mine and still been contaminated with asbestos. The confusion arises mostly because both vermiculite and asbestos are used as an insulating material. That was just an unfortunate coincidence.


Go ahead and use vermiculite without fear. Itís still your friend.