There are several asbestos forms; all are fibrous in nature, which is why they are so easily inhaled. There are six minerals that are defined as "asbestos" including: chrysotile, amosite, crocidolite, tremolite, anthophyllite and actinolite. Chrysotile is the mineral most commonly used to make asbestos products used in United States building materials. When mined and processed, these minerals become such small fibers that they are not visible to the naked eye. Asbestos fibers were commonly used to make insulation as well as ceiling and floor tiles. The product was widely used for many years as a building material because it was inexpensive, was fire retardant, was strong and was great at absorbing sound. Asbestos first became regulated as a hazardous substance in the United States under the Clean Air Act of 1970. Today, asbestos is no longer used as a building material. However, there are still buildings out there which contain asbestos materials.