Most asbestos exposure is the result of industrial use as well as construction, ship building, electronics, automotive manufacture and servicing, aviation...the list goes on and on and on.
What is generally not widely spoken of however asbestos exposure due to natural causes.
I should probably start out by explaining that there is not a single mineral known as "asbestos." Asbestiform is a generic term that geologists use to describe several different minerals that vary in chemical makeup. What they all have in common is their flexible, fibrous characteristics. There are in fact over a dozen different minerals that may be classified as asbestos, though only three of these were ever used widely in commercial applications and subject to regulation.
It is impossible however to regulate nature (which doesn't stop some people from trying – but that's a whole other rant). Although most asbestiform mineral deposits on the planet are locked away in the ground, there are a few outcroppings. One of these is a region in eastern Turkey around the village of Karain; for hundreds of years, buildings and roads have been made from a local stone containing an asbestiform mineral known as zeolite. Mesothelioma is the leading cause of death in the area, affecting as much as half the population.
Here in the U.S.A., there's California. A few years back, a reported in Mother Jones published a story about an upscale suburb located in the Sierra foothills east of Sacramento that was built atop a massive serpentine deposit – something the developers and homebuilders of El Dorado neglected to mention to home buyers.
Ironically, serpentine – the source of common "white" (chrysotile) asbestos is the Golden State's official rock. And according to the most recent U.S. Geological Survey, there's plenty of it right near the surface in 48 California counties, including densely-populated Los Angeles, Orange and San Diego.
It's not all chrysotile, the so-called "safe" form of asbestos ("safe" because until recently, it was not associated with asbestos cancer – a perception that recent medical research is now changing). The California state geological survey revealed the presence of "hard" amphibole asbestos outcroppings in Los Angeles, San Francisco, San Diego and Fresno counties.
Koonz, Heidi. "New Map Shows Locations of Naturally Occurring Asbestos in California." U.S. Geological Survey (http://www.usgs.gov/newsroom/article.asp?ID=2888 ). Released 22 August 2011.
Patterson, Randall. "Not In Their Back Yard." Mother Jones, May/June 2007.
Van Gosen, Bradley S. et. al. "Reported Historic Asbestos Mines, Historic Asbestos Prospects, and Other Natural Occurrences of Asbestos in California." California Geological Survey, 2011.