Friability (or friable) is the ability of a solid substance to be reduced to smaller pieces with little effort. The opposite of friable is indurated.
Often, substances designated as being hazardous, such as asbestos or crystalline silica are referred to as being friable if they are present in such a state that it is possible for small particles to easily become dislodged, thus enabling them to become respirable (able to enter human lungs), posing a health hazard.
A friable substance is any substance that can be reduced to fibres or finer particles by the action of a small pressure or friction on its mass, such as inadvertently brushing up against the substance. The term could also apply to any material that exhibits these properties. Examples include but are not limited to:
Tougher substances, such as concrete may also be mechanically ground down and reduced to finely divided mineral dust. However, such substances are not generally considered friable because of the degree of difficulty involved in breaking the substance's chemical bonds through mechanical means. Some substances, such as polyurethane foams, can increase in friability with exposure to ultraviolet radiation (such as is present in sunlight).
Friable and indurated are terms used commonly in soft-rock geology, especially with sandstones, mudstones and shales to describe how well held together or cemented the rock is.
The term "friable" is also used to describe tumors in medicine, with tumors that are easily torn apart having a higher risk of malignancy and metastasis.