Asbestos is a mineral that occurs naturally in metamorphic and igneous rocks. Asbestos differs from other minerals in the way its crystals are formed. In asbestos the crystals take the form of long thin fibres. These fibres can released from the rock by crushing followed by blowing. The asbestos fibres released are strong, flexible and, most importantly, non-flammable. Fibres that are at least 1 cm (0.4 inch) in length can be spun into yarn. Shorter fibres can be used is other products as paper, millboard, and asbestos-cement building materials.
Asbestos is heat, fire, alkali and acid resistant, an excellent heat insulator and inexpensive to produce. Originally it was regarded as a miracle material, combining the strength of rock with the flexibility of silk.
Asbestos is divided into two mineral groups “Serpentine” and “Amphibole”. The crystalline structure in the Serpentine group takes the form of a sheet or layered structure. Amphiboles have a chain-like structure.
There are three common types of fibrous asbestos in commercial use:-
This is the only member of the Serpentine group of minerals. It is actually white-gray in colour, silky, flexible and very strong. Most of it comes from Canada ( three quarters of the worlds chrysotile is found in the province of Quebec). It is the most common form of asbestos found in buildings but it is also used in asbestos textiles.
This is a member of the amphibole group. Most of it comes from Southern Africa (“Amosite” – stands for the “Asbestos Mines of South Africa) but some is also found in Australia. It is the second most common form of asbestos found in building materials, often in thermal insulation.
This is another amphibole found in Southern Africa, less brittle than brown asbestos. It is often used in asbestos textiles and high temperature applications. Because of health hazards associated asbestos use, it is now illegal to import or supply in the UK any of these three common types of asbestos.
Unfortunately the first ban on asbestos was only introduced in 1985. Import of white asbestos was banned as late as 1999 and there are still products in which it can be legally used in the UK.
Before these controls were introduced huge quantities of all types of asbestos were used in the UK. This has given rise to a legacy of health problems for those who came, (and continue to come), into contact with it.