Its when it becomes friable and releases airborne particulate matter that is respirable in size (Gets past the cilia then into the lungs) if you start smashing the stuff with a hammer or friction saw that's when the issue really arises these particles can penetrate right into the lungs gas exchange alveoli which is where the real damage occurs.
Blue asbestos was mined in West Au at Wittenoom gorge (Now a ghost town) there was an extensive court battle involving the James Hardy Company that they knew the risks posed to the workers from Blue Asbestos it went on for years and allot of the affected workers died before finally the High Court of Australiamade the company pay large compensation payments whats the point of money when your stuck to an O2 bottle wheezing away dying a slow death!!!!