By Linnaea Weld
When we brainstorm “What’s in Your Watershed” topics, we normally come up with animals. From coyotes to white sturgeon, we’ve brought you some fascinating facts about fantastic fauna. However, in our education programs, we teach our students that watersheds are made up of both biotic and abiotic factors. We emphasize that both living and nonliving things are important to how a watershed looks and functions. So this month, we are going to celebrate one of the more underappreciated, but definitely important, aspects of our local watersheds: serpentinite.
Serpentinite is the state rock of California, and it is an important component of many habitats in the Bay Area and all over central and northern California. The rock is generally blue or green in color, due to the minerals present. Technically speaking, the term serpentinite refers to rocks made up of minerals in the serpentine group. These minerals are rich in magnesium silicate. Silica molecules form sheets of loose bonds, giving the rock a greasy or waxy feel and causing the rock to break easily.
Serpentinite is a metamorphic rock. Metamorphic rocks are formed when intense heat or pressure, or a combination of the two, are applied to existing rocks. In the case of serpentinite, the rock formed at tectonic boundaries where two plates meet. Scientists believe that the rock formed at a subduction zone, where an oceanic plate was being dragged under a continental plate. The ocean water was heated up and forced into the structure of existing magnesium-rich rock. This process formed serpentine minerals, changing an existing rock into serpentinite. While the rock is formed deep in the earth at the subduction zone, the process of hydrating the rock makes the serpentinite buoyant, and the rock essentially floats up through the mantle to the surface. The rock’s slippery surface aids in this process.
Why is serpentinite important to our watersheds? For one thing, this rock influences soil composition and what plants grow. Serpentinite is often bedrock. The rock is low in nutrients, so the plants that grow from serpentinite soils are specifically adapted to low nutrient soils and are very unique. In certain areas around California, including Redwood Regional Park in Oakland, serpentinite prairies have formed. These prairies are key locations for California’s native plants, hosting an estimated 13% of endemic species. Among these endemic species is the presidio clarkia (Clarkia franciscana), which only grows in the Bay Area.
There has been some dispute about the presence of asbestos in serpentinite. The California legislature debated removing serpentinite as the state rock due to the potential presence of asbestos back in 2010. Asbestos is cylindrical fibers, and when these fibers are inhaled in powder form, asbestos can harm the lungs. One mineral in serpentinite, chrysotile, can crystallize into the form of asbestos. However, not all serpentinite contains asbestos, and the fiber must be inhaled in the powder form, so the rock itself cannot harm us. In general, serpentinite is a harmless and beautiful abiotic factor in our watershed.
Next time you are out, keep an eye out for our lovely state rock and notice how it supports and structures our watersheds.