Vermiculate mined in Montana has been shown to be the cause of numerous mesotheliomas - not due to the vermiculite, but caused by the presence of other fibrous minerals in the vermiculite which possess properties very similar to asbestos. To the best of my knowledge perlite has never been shown to be associated with pneumoconiosis or other related lung disorders, even in miners with up to 20 years exposure. Perlite has been characterized by several sources (ACGIH, OSHA, etc.) as a nuisance or inert dust. Exposure to such dusts can sometimes result in temporary physical irritation, discomfort, impaired visibility, and enhancement of accident potential, but not to health impairment. Inhalation over long periods of high concentrations of any nuisance dust are undesirable as it may interfere with the lung clearance mechanism. In addition, coughing and temporary irritation and inflammation of the eyes, throat and nasal passages can occur as a result of overexposure. Repeated handling or contact may also result in some drying effects of the skin or slight skin abrasions as might occur with any mineral dust. In similar vein, the following is excerpted from a Materials Safety Data Sheet which must accompany all 'chemicals' when shipped/sold. "Summary: Perlite is a naturally occurring volcanic glass consisting of fused sodium*potassium*aluminum silicate. OSHA has classified perlite as a Particulate Not Otherwise Regulated (PNOR), which has the same Permissible Exposure Limit (PEL) as that used for nuisance and inert dusts. Although there are no published reports of adverse health effects from exposure to perlite dust, dust levels should be maintained below the OSHA PEL for PNORs and respirators should be used when airborne dust is present. Excessive inhalation over long periods of time may cause harmful irritation. Perlite is considered a nuisance dust by ACGIH. Medical conditions which may be aggravated: pre-existing upper respiratory and lung disease such as, but not limited to bronchitis, emphysema and asthma. Target Organs: Lungs, eyes. Route of Entry: Inhalation, dust contact with the eyes. Acute Health Effects: Transitory upper respiratory irritant. May cause coughing or throat irritation. Chronic Health Effects: Excessive inhalation of any mineral dust can overload the lung clearance mechanism." If we stick to the facts it makes it a lot easier for folks to make objective and reasonable decisions. J. Dr John T Lonsdale Zone 6b