Many serpentinites have a fibrous appearance like this one from Vermont. There can be two factors driving this appearance; first, these rocks are so soft that they can deform easily in response to the stresses of mountain building. In that case, these lines are slickenlines, reflecting one part of the rock grinding against another. Alternatively, some (But not all) serpentine minerals can grow in a habit where they form long needles; minerals that grow in this habit are lumped together as asbestos minerals. Serpentine-bearing rocks therefore can naturally host asbestos, and mines in the area where this rock came from in Vermont produced asbestos for more than half a century. Serpentinite rocks and serpentine minerals are most often found where little bits of Earth’s mantle get thrust up onto the continent, creating a feature we call an ophiolite. These are commonly produced when continents collide or when continents run into island arcs, as a bit of the mantle gets trapped in the collision zone. The serpentinites in Vermont are the remnant of the Taconic Orogeny, a mountain building event 440 million years ago where a volcanic island arc was thrust upon what is today New England, folding and faulting much of the area in the process. -JBB Image credit: James St. John https://flic.kr/p/2iE3pj4Reference https://bit.ly/2BhQPrk Previous TES series on Asbestos and health problems: https://www.facebook.com/TheEarthStory/photos/a.352867368107647.80532.352857924775258/778584158869297