Asbestos is a term used for several types of naturally-occurring fibrous minerals found in many parts of California.  The most common type of asbestos is chrysotile, but other types are also found in California.  When rock containing asbestos is broken or crushed, asbestos fibers may be released and become airborne.  Exposure to asbestos fibers may result in health issues such as lung cancer, mesothelioma (a rare cancer of the thin membranes lining the lungs, chest and abdominal cavity), and asbestosis (a non-cancerous lung disease which causes scarring of the lungs).  Sources of asbestos emissions include: unpaved roads or driveways surfaced with ultramafic rock, construction activities in ultramafic rock deposits, or rock quarrying activities where ultramafic rock is present.  To address some of the health concerns associated with exposure to asbestos from these activities, the Air Resources Board has adopted two Airborne Toxic Control Measures.