The Washington Division of Geology and Earth Resources provides maps and geologic information on minerals related to environmental and public health issues. The presence of certain elements, such as naturally occurring arsenic, asbestos, mercury and uranium can make exposure to the rocks that contain them hazardous. For example, radon gas is often associated with two-mica granites that contain radioactively decaying uranium. Much of DGER’s information on hazardous minerals shows locations of historic mines and prospects or geologic formations that are more likely to contain these and other minerals that can pose health hazards. DGER Bulletin 37 contains a helpful overview on all minerals known to occur in Washington state.
Asbestos is the general term for a number of minerals belonging to the serpentine and amphibole groups that have similar properties. These include chrysotile, Mg3(Si2O5)(OH)4, a member of the serpentine group, and the amphiboles including fibrous varieties of tremolite, Ca2Mg5Si8O22(OH)2, actinolite, Ca2(Mg,Fe)5(Si8O22)(OH)2, crocidolite (riebeckite), Na2Fe2+3Fe3+2Si8O22(OH)2, anthophyllite, (Mg, Fe)7Si8O22(OH)2, and amosite, an iron-rich anthophyllite. Asbestos is frequently associated with serpentinite and partially serpentinized ultramafic/ultrabasic rocks(however, not all ultrabasic rocks are serpentinite bearing). Asbestiform minerals are composed of very thin, long fibrous crystals, and it is this fibrous nature that makes them dangerous. If asbestos disintegrates, the microscopic thread-like fibers are released into the environment and can then be inhaled or otherwise ingested (through drinking water, for example), causing lung cancer and other respiratory diseases.
Magnified view of chrysotile asbestos from Chelan County. Image taken
by David K. Norman, DNR.
Asbestos occurs naturally in certain geologic settings in Washington but is most common in the ultrabasic/ultramafic rocks shown in the map below. There have been no commercial deposits or asbestos mines in Washington but there are many occurrences. In addition to the location of the ultramafic formations, the map below shows other known occurrences of asbestos in Washington State. Note: There is much work to be done on this topic and further study is necessary to understand naturally occurring asbestos in Washington. The chrysotile asbestos pictured above is from the Lake Wenatchee area of Chelan County.
Known asbestos occurrences (purple dots) and ultramafic formations (purple regions) in Washington State.
For more information about the ultramafic formations shown above visit the Washington State Geological Information Portal.
Click here for a more detailed 1 page map of the naturally occurring asbestos locations of Washington.
For more information on asbestos health risks, visit Washington State Department of Health's webpage on asbestos.
Mercury, called quicksilver by miners, is a silver white heavy metal (heavier than lead) which is liquid at room temperature. It is typically extracted from the mineral cinnabar, HgS (pictured below), by heating the crushed ore. Mercury is highly toxic and can be absorbed through the skin or inhaled as mercury vapors, poisoning the victim. Mercury may also enter the food chain and become a health hazard to animals and humans. It is a constituent of fluorescent lighting, including compact fluorescent light bulbs (CFLs), which are widely used in homes and businesses due to their longevity. Special care should be taken when disposing of burned out fluorescent bulbs. More information can be found through the Washington State Department of Ecology.
Image of cinnabar taken by R. Weller/Cochise College
Mercury was mined historically in Washington at only a few locations, most importantly near Cinebar in Lewis County, which takes its name from the principal ore of mercury. This is discussed at length in the Report of Investigations No. 6: Relation of Geology to Mineralization in the Morton Cinnabar District. Its principal use in this state was in the recovery of placer and lode gold. Known occurrences of mercury in Washington State are shown on the map below.
Known mercury occurrences in Washington State.
For more information, visit Washington State Department of Health's webpage on mercury.
Arsenic can occur naturally in many rocks and minerals and is generally associated with sulfur. The most common arsenic minerals are arsenopyrite, FeAsS, (46.0 % arsenic), and the sulfides, realgar, AsS (70.1 % Arsenic), and orpiment, As2S3 (61.0% arsenic). Arsenic has a variety of commercial uses from industrial (metallic alloys), to agricultural (pesticides) to medical (pharmaceuticals), and is commonly used in the manufacture of semiconductors. Until recently, arsenic had widespread use as a treatment for lumber used as building material. Arsenical minerals are commonly found in piles of finely ground sand, or “tailings,” around metal mines that had a concentrating mill. In addition to arsenic, tailings often contain other heavy metals such as lead in galena (PbS), copper in chalcopyrite (CuFeS2) and zinc in sphalerite (ZnS). These minerals can cause respiratory problems when inhaled, particularly at mine sites that are popular for motorized recreational vehicle use. Additionally, water discharged from metal mine openings may contain these same minerals in solution and present a health hazard to humans and animals. Arsenic is especially dangerous when it contaminates groundwater and poisons drinking water.
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Sample of orpiment and realgar.
R. Weller/Cochise College
United Copper Mine, Stevens County, WA.
F. Wolff, DNR
Monte Cristo Mine, Snohomish County, WA.
F. Wolff, DNR
Arsenic minerals occur naturally and are widely distributed in mining districts throughout Washington (see map below). Gem quality orpiment and realgar have been collected from deposits along the Green River in King County. The best known arsenical ores are in the Monte Cristo district in Snohomish County, where arsenopyrite was mined for gold and silver extraction. Many of the arsenic-bearing ores were shipped to the ASARCO Smelter in Tacoma, WA. A 1997 Washington Geology article gives a brief description of the mineralogy of the slag at the Tacoma smelter.
Known arsenic occurrences in Washington State.
For more information, visit Washington State Department of Health's webpage on arsenic.
Uranium & Radon
The radioactive element uranium occurs naturally in very small amounts (parts per million) in rocks, soils, and water. The half-life of its most common isotope, 238U, is approximately 4.5 billion years, making it ideal for radiometric dating of the oldest rocks on Earth. It is also used to produce military-grade ammunition and to fuel nuclear power plants. The most common ore of uranium is uraninite (UO2), which is mined in a variety of ways including open pit, underground, and leach mining (using alkali or acid as extractor chemicals). Disease caused by direct exposure to uranium is relatively rare, although workers who produce phosphate fertilizer, or residents who live in close proximity to nuclear weapon testing sites, uranium mines, or uranium processing or enrichment plants are at risk. Uranium can enter the body by inhaling contaminated dust or by ingesting it through contaminated water and food. However, the primary danger posed by naturally occurring uranium is the release of radon gas into the environment. Radon is carcinogenic and a prominent cause of lung cancer. Radon is produced by natural radioactive decay of uranium (and/or thorium) and is particularly associated with uraniferous two-mica granites. Radon is colorless, odorless, and tasteless, making it exceptionally hazardous, as its presence is revealed only by specific detectors. Structures built over radon-emitting granites can trap and concentrate the gas, putting the inhabitants at extreme risk. (Note that “granite” countertops use the term granite loosely. Most are not uraniferous and most are not granite.) Uranium mill tailings, mine dumps and mine water are also sources of radon gas, making miners especially vulnerable.
Uranium deposits have been observed in Washington State east of Puget Sound, and particularly in the northeast quadrant of the state (see red areas on the map below). Two commercial uranium mines in Stevens County Washington, the Midnite Mine and the Sherwood Mine, ceased production in the early 1980s and entered the reclamation phase. Reclamation of the Sherwood Mine was completed in 2000. Cleanup of the Midnite Mine superfund site (now led by the US EPA) is ongoing.
Radon hazard classification, based on 1:100,000-scale geologic mapping, and known uranium sites in Washington State.
Radon test measurement density in Washington State.
More information on uranium mines is available through the US EPA and the US Bureau of Land Management.
Information about the Midnite Mine
Information about the Sherwood Mine
For more information about radon visit the Washington State Department of Health, the Washington Tracking Network and the US EPA radon webpages.