Gallery of Slickensides

01
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Slickensides on a Hand Specimen

The telltale glint
Gallery of Slickensides or Fault Mirrors. Photo (c) 2013 Andrew Alden, licensed to About.com (fair use policy)

Slickensides are naturally polished rock surfaces that occur when the rocks along a fault rub against each other, making their surfaces smoothed, lineated, and grooved. Their formation may involve simple friction, or if the fault surface was once deeply buried, actual growth of oriented mineral grains may respond to the forces on the fault. Slickensides appear to lie between the grinding of shallow rocks that makes fault gouge (and cataclasite) and the deep-seated friction that melts rock into pseudotachylites.

Slickensides may be scattered surfaces as small as your hand or, in rare cases, thousands of square meters in extent. The corrugations show the direction of motion along the fault. Unusual minerals may occur given the combinations of fluids and pressures along slickensides. But even familiar rocks, as we will see, take on unusual features too.

Slickensides can range in size from tiny, as in this chert specimen, to gigantic. In all cases, you spot them by their telltale glint, and in all cases they signify shear, the sideways motion of faulting.

02
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Slickensides on an Outcrop

Look toward the sun
Gallery of Slickensides or Fault Mirrors. Photo (c) 2013 Andrew Alden, licensed to About.com (fair use policy)

Slickensides may appear on an outcrop if you face the sun. This is part of the faulted and sheared western face of Point Bonita in Golden Gate National Recreation Area, near San Francisco.

03
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Slickenside in Limestone

We'll start small
Photo (c) 2008 Andrew Alden, licensed to About.com (fair use policy)

Most rock types can have slickensides. This limestone is also fractured and brecciated by the fault movements that created this slickenside. (click for closeup)

04
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Slickenside in Sandstone, Wright's Beach, California

An uncommon host rock for slickensides
Gallery of Slickensides or Fault Mirrors. Photo (c) 2010 Andrew Alden, licensed to About.com (fair use policy)

This site is very close to the San Andreas fault, and pervasive fracturing affects this already-jumbled tectonic megabreccia of Franciscan sandstone.

05
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Slickenside in Peridotite, Klamath Mountains, California

Serpentine slips in peridotite
Slickensides or Fault Mirrors. Photo (c) 2009 Andrew Alden, licensed to About.com (fair use policy)

Serpentine minerals form easily by alteration of peridotite, especially where faulting admits fluids. These readily form slickensides.

06
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Slickensides in Serpentinite

Pervasive slickensides
From stop 19 of the California subduction trip. Photo (c) 2006 Andrew Alden, licensed to About.com (fair use policy)

Slickensides are very common in serpentinite. These ones are small, but whole outcrops glisten because slickensiding is so pervasive. (See serpentinite gallery)

07
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Slickenside in Serpentinite Outcrop

Outcrop-scale slickenside
Slickensides or Fault Mirrors. Photo (c) 2008 Andrew Alden, licensed to About.com (fair use policy)

This larger slickenside is in a serpentinite body at Anderson Reservoir, California, near the Calaveras fault.

08
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Slickenside in Basalt

A rare black flash
Slickensides or Fault Mirrors. Photo (c) 2009 Andrew Alden, licensed to About.com (fair use policy)

Where igneous rocks are tectonically deformed, as at this outcrop in northern San Quentin, California, even basalt can acquire slickensides.

09
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Closeup of Basalt Slickenside

A dark mirror
Slickensides or Fault Mirrors. Photo (c) 2009 Andrew Alden, licensed to About.com (fair use policy)

This sample from the previous outcrop displays the aligned mineral grains and polished surface that define a slickenside. (click full size)

10
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Slickenside in Metabasalt, Isle Royale, Michigan

Don't mistake these for striations
Gallery of Slickensides or Fault Mirrors. Photo courtesy Ben+Sam of Flickr under Creative Commons license

This exposure from Raspberry Island can be mistaken for glacial striations, but the orientation is wrong. The green color is suggestive of serpentine minerals.

11
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Slickenside in Chert

Overview of the outcrop
Slickensides or Fault Mirrors. Photo (c) Andrew Alden, licensed to About.com (fair use policy)

In San Francisco's Corona Heights near Peixotto Playground at 15th and Beaver streets is this world-class slickenside in Franciscan chert, exposed by quarrying.

12
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Corona Heights Slickenside, Beaver Street

Right in an urban neighborhood
Photo (c) Andrew Alden, licensed to About.com (fair use policy)

On the Beaver Street end of this slickenside, the higher surfaces reflect the sky. Slickensides are also called fault mirrors.

13
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Slickenlines

Showing the direction of fault motion
Photo (c) Andrew Alden, licensed to About.com (fair use policy)

The individual streaks and grooves of a slickenside are called slickenlines. Slickenlines point in the direction of faulting, and some features can indicate which side moved which way.

14
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Rock Near a Slickenside

A bit of the fault's other side
Photo (c) Andrew Alden, licensed to About.com (fair use policy)

A remnant block from the near side of the fault plane shows the undisturbed form of the chert.

15
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Slickenside at Arm's Length

Closer look at polished sections
Photo (c) Andrew Alden, licensed to About.com (fair use policy)

Patches of the slickenside surface gleam blue in skylight. Motion along this surface took place over millions of years.

16
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Polished Chert

Looking its natural best
Photo (c) Andrew Alden, licensed to About.com (fair use policy)

The brown Franciscan chert on the slickenside was once a deep-sea ooze; learn more in the California subduction tour.

17
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Chert Reflections

Sky reflected in stone
Photo (c) Andrew Alden, licensed to About.com (fair use policy)

The slickenside surface appears hand-polished. Chert is tough enough to preserve this kind of polish against weathering.

18
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Slickenside in the French Alps

Another huge exposure
Photo courtesy Centre National de la Recherche Scientifique

Large slickenside on the Vuache fault, at Mandalaz peak in Haute-Savoie.

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Your Citation
Alden, Andrew. "Gallery of Slickensides." ThoughtCo, Feb. 28, 2017, thoughtco.com/gallery-of-slickensides-4122857. Alden, Andrew. (2017, February 28). Gallery of Slickensides. Retrieved from https://www.thoughtco.com/gallery-of-slickensides-4122857 Alden, Andrew. "Gallery of Slickensides." ThoughtCo. https://www.thoughtco.com/gallery-of-slickensides-4122857 (accessed November 23, 2017).