Serpentinite from the Klamath Mountains, California (sample courtesy of Hannah Scherer; photo from Brian Romans)

A bill introduced by California State Senator Gloria Romero in February 2009, the language of which was completely gutted and then amended in April of this year, would “remove serpentine as the state rock and lithologic emblem and would leave the state rock unspecified.” Why introduce a bill to the state assembly devoted to removing the state rock? The primary reason, as stated in the bill, is because “serpentine contains the deadly mineral chyrsotile asbestos, a known carcinogen, exposure to which increases the risk of cancer mesothelioma.” Supporters of the bill include cancer awareness groups and other groups representing those dealing with mesothelioma.

While we are all entitled to our own opinions, we are not entitled to our own facts. In that spirit, I think some basic geologic facts are in order:

•    Firstly, “serpentine” refers to a group of minerals, not a rock. The term “serpentinite” is the proper term for the rock that is mostly made up of one or more of the serpentine group minerals.

•    Serpentinite is a metamorphosed version of rocks that make up oceanic crust after they are incorporated into subduction zones (plate boundaries where oceanic plates are thrust under continental plates). The recognition and study of serpentinite in California contributed to the understanding of modern plate tectonic theory.

•    Serpentinite has a unique association with California for many reasons including: its association with gold deposits and the resulting California Gold Rush history, many plants unique to California grow on serpentinite-rich soils, the fact that serpentinite is thought to promote slow (and less hazardous) ‘creep’ along faults, and others.

•    There is no such mineral as “chrysotile asbestos”; there is a mineral “chrysotile” that crystallizes into a fibrous material referred to as asbestos but not all varieties of serpentinite contain it.

•    The term “asbestos” does not have a unique mineralogical association; it is derived from the term that describes the fibrous nature.

•    Varieties of asbestos from a completely separate group of minerals, called the amphibole group, are considered to be the most dangerous form.

•    The health danger of asbestos is when people breathe the powdered form into their lungs — and not just once or twice, but chronically over many years.

•    Bottom line: walking on, being near, handling, or even eating a piece of serpentinite rock is NOT harmful.

As one blogger put it, the only way a piece of serpentinite might be harmful is if someone hurled a piece at you. To reiterate, one must inhale the powdered version into their lungs for it to be harmful. The wording of the bill is such that it’s not surprising there is some confusion and misunderstanding. Some of the mainstream reporting about this bill has failed to communicate that exposure to the rock serpentinite is distinct from exposure to the powdered form of a component mineral that might be in the rock. This is an important distinction.

Supporters of this bill argue that having a rock with an association with harmful derivative materials is inappropriate for a state symbol. One of the more interesting bits of history I’ve learned following this story is that the original 1965 proclamation of serpentinite as the state rock was motivated by a desire to highlight its economic and commercial importance as a source of mined asbestos. However, the connection between the mining process and harmful effects were discovered thereafter and asbestos mining was banned in California in the 1970s. So, why is the issue coming up now? It’s unclear to me.

The final point I’ll make about this issue, which is something many other geologists have made as well, is that what’s most important here isn’t to maintain serpentinite as the state rock at all costs. What’s important is that the proposal deserves a fair and open debate. If the state assembly feels that spending the time and resources to do that isn’t in California’s best interests at this time, then simply table the bill and deal with it at a later date.

PDF of Senate Bill No. 624

Much of the information presented in this post comes from the educating and advocacy about this issue by geoscience educator Garry Hayes at his blog Geotripper, Bay Area science writer Andrew Alden at, and environmental historian Jon Christensen from the Bill Lane Center for the American West at Stanford University.

Learn the Facts About Serpentinite Before It’s Removed as California’s State Rock 2 October,2015Brian Romans


    I enjoyed this article’s many facts and information on what seems to be quite an important “rock”, both geologically and historically. I was drawn to this article because I have collected many samples while hiking throughout California and have always enjoyed how beautiful it is. I absolutely agree that before people take such Serpitinite off the list they should learn more about it and why it is worthy of such a title.

  • We at the Committee for Green Foothills have officially opposed SB 624:

  • Debbie Irvin

    I love this rock — I’m lucky enough to have been given a number of very large samples for my classroom. It’s part of what makes California so interesting and unusual, geologically speaking!

  • andrew

    what is the minerals streak

  • brie-anna

    what is serpentinites texture and structure ??

  • Lola Themola

    As I understand it, what we normally call asbestos, which causes asbestosis, can be caused by one fibre in the lungs. That is not the same kind of asbestos-type material in serpentinite. But, serpentinite can be naturally in a form that you can inhale. any grinding, walking on, or fooling around with serpentinite can cause “fibres” to break off and become available for inhalation. So, let’s keep the rock (removing it as the state rock is pretty silly) but stay clear of it when you can.


Brian Romans

Brian Romans is the author the popular geoscience blog Clastic Detritus where he writes about topics in the field of sedimentary and marine geology and shares photographs of geologic field work from around the world. He is fascinated by the dynamic processes that shape our planet and the science of reconstructing ancient landscapes preserved in the geologic record. Brian came to the Bay Area in 2003 and completed a Ph.D. in geology at Stanford University in 2008. He lives in Berkeley with his wife, a high school science teacher, and is currently working as a research scientist in the energy industry. Follow him on Twitter.

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