text: Since you asked this question in earth sciences and geology category, I will assume that you are interested in the kind of dust that gets blown around in the wind, and so forth. \nThe great volume of this dust is formed by erosion (water, wind, ice) of soil, lake beds, and rocks. Clay particles are an especially abundant component of dust--because of they can be small enough to be easily picked up by wind.  But, dust can also contain anything else of the right size (small, light). USGS analysis of dust samples collected at monitoring stations shows that the African dusts can carry pesticides, heavy metals (such as mercury and arsenic), naturally occurring radioactive isotopes, pollen, insects, miscellaneous organic debris, smoke, and pathogenic viruses, bacteria, and fungi.\nArid environments generate big dust clouds at time because there are not many plants holding the surface down. Africa and the dry parts of China, for example, may generate big plumes of dust. Known dust sources in the SW USA include dry lake (playa) surfaces and their margins, ephemeral drainage areas, poorly vegetated alluvial fans, agricultural fields, military bases, and growing urban and rural areas. \n\nhttp://esp.cr.usgs.gov/info/dust/\nhttp://health.usgs.gov/inhalation/african_dust.html\nhttp://esp.cr.usgs.gov/info/sw/monitor/dust.html