Rocks as insulators

Asbestos is a material that was frequently used as an insulator in the past. In fact, asbestos is particularly resistant to high temperatures, and it is used for the production of cartons, fabrics and fireproof ropes. Since 1994 any use of asbestos has been prohibited, as this material releases hazardous fibres into the air, provoking serious diseases to the respiratory system. Vermiculite and perlite have been used more recently. Vermiculite is a mineral that is extremely full of water and that is “expanded” as a result of heating at 900 – 1000°C. In this way the water is rapidly expelled and the mineral, that becomes extremely light, can be used as an insulating infill for wall cavities (the space between two nearby walls that is created in order to be filled with insulating material). Perlite is an effusive rock that is used for plaster together with chalk, cement and lime. Also pumice, a volcanic rock that is full of cavities, is often used as a thermal and acoustic insulator, after being milled and mixed to mortars.
Some types of basalts are melted at 1300 °C in order to obtain a particular vitreous material that is called “mineral wool”. This material is used as a thermal insulator, as it has the capacity to resist at temperatures around 1000 °C. Since it is an excellent acoustic insulator, it is widely used in modern buildings.

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