Asbestos is a general name given to several naturally occurring fibrous minerals that have crystallised to form long thin fibres. They are divided into two sub-groups: serpentine (chrysotile (white asbestos)), which was the most commonly used type of asbestos and amphiboles, which includes crocidolite (blue asbestos), amosite (brown asbestos), tremolite, actinolite and anthophyllite, of which crocidolite was the most commonly used. Blue and brown asbestos are considered to be the most dangerous. The importation, supply and use of white, blue and brown asbestos have been banned. Asbestos fibres do not dissolve in water or evaporate; they are resistant to heat, fire, chemical and biological degradation and are mechanically strong. Such properties made it an ideal material for use in a number of products, including insulation material for buildings, boilers and pipes; insulating board to protect buildings and ships against fire; asbestos cement for roofing sheets and pipes. The amount and type of asbestos found in the fabric of buildings depends on the product. Crocidolite and amosite were used for lagging up to 1960s. Asbestos-cement products contain 10-15% asbestos fibre, generally chrysotile. Asbestos containing products found in fires include roof tiles and asbestos-bitumen roof coatings.