Which is the least commonly found type of asbestos?

The least commonly found type of asbestos is tremolite. Tremolite is much rarer in commercial products compared to other asbestos types. While chrysotile, also known as "white asbestos," is the most widely used type of asbestos, and it accounts for the majority of asbestos found in buildings, amosite ("brown asbestos") and crocidolite ("blue asbestos") are also more commonly found in various industrial applications and insulation materials.

Crocidolite is known for its high durability and resistance to heat, which made it a popular choice for certain products, while amosite was widely used in cement sheets and insulation. Tremolite, on the other hand, is mostly found in a more natural state and is less frequently associated with products, leading to its classification as the least commonly encountered type of asbestos in terms of industrial applications and asbestos-containing materials.

The rarity of tremolite in commercial contexts underscores its distinction from the more prevalent varieties, making it the correct answer in this question.