Asbestos mineral (white), with a pencil tip for scale. Asbestos refers to six natural silicate minerals in the serpentine and amphibole classes. All have a form of thin, fibrous crystals. The different forms of asbestos differ in their composition and the health hazard they pose when inhaled. Asbestos has been widely used for its excellent insulating and heat-resistant properties. This sample is of chrysotile, the most dangerous form of asbestos, here associated with dark grey graphitic rock. The sample is from the Kaisersberg, near Leoben, Austria.