Serpentine is a hydrated magnesium silicate mineral group, not a single substance. Only one specific mineral within this group is classified as asbestos. Asbestos is a commercial term describing six naturally occurring fibrous silicate minerals known for their high tensile strength and heat resistance. The most common form of commercial asbestos, chrysotile, is a fibrous variety of the serpentine mineral group.
The Serpentine Mineral Group
Serpentine is a group of about twenty related minerals that form a major component of the earth’s crust. These minerals are characterized by a sheet silicate structure, where their atoms are arranged in layers. Serpentine minerals form through serpentinization, a process where ultramafic rocks like olivine and pyroxene chemically react with water at low temperatures.
The most common non-fibrous members of this group are antigorite and lizardite. These minerals form massive rock known as serpentinite, which often features a mottled green appearance. Serpentinite is widely used as a decorative or architectural stone. The vast majority of naturally occurring serpentine rock is composed of these non-fibrous forms.
The Specific Link to Asbestos
The direct link to asbestos is through chrysotile, the only member of the serpentine family classified as asbestos. Chrysotile is structurally different from non-fibrous relatives because its layered structure curls into microscopic, hollow tubes, creating a fibrous form. This fibrous nature made it commercially valuable and led to its classification as “white asbestos.”
Chrysotile historically accounted for 90 to 95 percent of all asbestos used commercially worldwide. Its flexible fibers were incorporated into numerous products, including brake linings, gaskets, and cement sheeting. The other five regulated forms of asbestos—amosite, crocidolite, tremolite, actinolite, and anthophyllite—belong to the amphibole mineral group. Amphibole minerals are chemically distinct from serpentine and are characterized by straight, needle-like fibers.
Natural Occurrence and Exposure Risk
Serpentine rock is commonly found in geological areas associated with tectonic plate boundaries, such as mountain ranges or ophiolite formations. When chrysotile is present in these formations, it is referred to as “naturally occurring asbestos” (NOA). The presence of serpentine rock does not automatically mean there is an immediate health risk.
The danger arises only when the rock is disturbed, releasing fine, airborne fibers that can be inhaled. Disturbance can happen through natural processes like weathering and erosion, or through human activities. Activities such as construction, grading, mining, or using serpentine rock for unpaved road material can crush the rock and liberate chrysotile fibers into the air. The risk of exposure is tied directly to the material’s friability and the potential for fiber release.
Identifying and Managing Potential Contact
Identifying naturally occurring asbestos visually is unreliable because the fibrous minerals are often mixed with non-fibrous serpentine and other rock components. The only definitive way to confirm the presence and type of asbestos is through laboratory testing conducted by accredited professionals. If you live in an area known to have serpentine rock, the general principle is to avoid disturbing the material.
For managing outdoor areas, practical steps focus on limiting dust-generating activities. This involves avoiding dry sweeping or using leaf blowers in areas with exposed rock or soil. Paving unpaved walkways or driveways and covering exposed soil with non-asbestos material can significantly reduce the potential for fiber release. Local environmental and health agencies often provide maps and specific guidance for managing properties in known NOA zones.